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Why is Southeast Asia becoming more vulnerable to nuclear risk even as it remains formally non-nuclear?

Southeast Asia’s Nuclear Weapon-Free Zone has long been treated as a stabilizing firewall in an otherwise volatile region. Yet despite the continued legal compliance and strong anti-nuclear norms, the region is increasingly exposed to nuclear danger.

Across East Asia, nuclear dynamics are shifting in ways that extend beyond overt weaponization. The most consequential changes stem from the diffusion of nuclear-adjacent capabilities across maritime strategy, civilian nuclear development, and conventional military competition. Prevailing assessments have largely only focused on flashpoints in Northeast Asia — particularly the Korean Peninsula — where North Korea’s expanding “nuclear shield and sword,” advances in submarine-launched ballistic missiles, and China’s accelerating nuclear modernization alongside Beijing’s military pressures on Taiwan have intensified deterrence pressures on U.S. allies. Concerns over hedging in South Korea and Japan amid questions about extended deterrence credibility underscore this landscape. Recent maritime developments — including Pyongyang’s pursuit of a nuclear-powered, nuclear-armed submarine, Washington’s agreement to assist Seoul with nuclear-powered submarine development, and new permissions for uranium enrichment and spent fuel reprocessing — have only sharpened pre-existing proliferation anxieties. Yet these northern dynamics have increasingly radiated southward.

Southeast Asia, also in the crosshairs of intensifying U.S.-Chinese rivalry and contested maritime spaces, has now been facing growing exposure to nuclear-powered and potentially nuclear-armed naval assets. China’s reported submersible ballistic nuclear submarine deployments into the South China Sea, sustained U.S. naval presence and freedom of navigation operations, and expanding anti-submarine warfare activities, alongside a brewing missile race are gradually transforming the region into a theater of nuclear-adjacent competition. Even conventional incidents occurring in such a volatile region may therefore have the potential to draw in strategic assets, raising escalation risks and complicating the Association of Southeast Asian Nations’ efforts to preserve their autonomy and cohesion.

At the same time, Southeast Asia’s energy landscape is also being reshaped by another slow yet consequential trend — a renewed interest and a growing acceptance of civilian nuclear technologies. Driven primarily by energy security concerns, decarbonization commitments, and developmental priorities, several Association of Southeast Asian Nations members — led by Indonesia, Vietnam, and the Philippines — have now been exploring nuclear power and related fuel-cycle capabilities framed as exercises of the right to peaceful use. These dual-use technologies, given their extensive reliance on external suppliers, and with potentially uneven regulatory capacity, may risk entangling civilian infrastructure with strategic rivalry.

Together, these trends signal an empirically new phase of nuclear risk which is defined less by overt proliferation than it is by latency, proximity, and nuclear-adjacent competition; in turn testing whether the global non-proliferation regime holds the space to adapt or erodes under cumulative strain.

As civilian nuclear development advances, Southeast Asia should prioritize strong domestic regulation, rigorous safeguards, and regional crisis mechanisms addressing external nuclear-powered naval activity. The policy imperative, therefore, is to modernize how the region operationalizes its non-nuclear commitments in an increasingly nuclear-adjacent strategic environment.

Shifting Equilibrium of Alliance Assurances: The Northern Flank and Context Setting

Developments on the northern flank of East Asia provide the strategic context.

Northeast Asia is already one of the world’s most concentrated nuclear-risk environments, where the overlapping presence of four nuclear-armed states — North Korea, China, Russia, and the United States — creates persistent instability. What makes this delicate environment even more consequential is not just material capability, but an incessantly weakening confidence in extended deterrence. More than rejecting the normative proliferation debate, the issue hence becomes about compensating for perceived gaps in deterrence credibility and crisis assurance.

For example, in Seoul, a more plausible driver of expanding fuel-cycle ambitions is strategic rather than commercial. Beyond just supporting prospective naval reactors, indigenous enrichment would materially shorten the timeline to a weapons option. Latency, in this sense then, is already infrastructurally embedded, and eventually steadily institutionalizing capabilities that reduce the political and technical distance to it. The legal evolution surrounding Seoul’s program, too, is therefore consequential. For instance, under the International Atomic Energy Agency’s comprehensive safeguards framework (Information Circular/153), nuclear material used for non-proscribed military activities — such as naval propulsion — may be withdrawn from routine inspection. For decades, U.S.-South Korean nuclear cooperation agreements had constrained this pathway by prohibiting military applications of transferred nuclear technology and tightly controlling enrichment and reprocessing. Even where international law created limited space, alliance arrangements had formerly reinforced restraint. The recent U.S. approval for South Korean nuclear-powered submarines, alongside support for expanded enrichment and reprocessing, however, marks a significant shift from that earlier posture.

Although naval propulsion, enrichment, and reprocessing are treated as legally distinct under bilateral agreements, their convergence creates a permissive structural environment. This means technologies that were historically viewed as proliferation-sensitive are reframed as legitimate components of alliance modernization. This obviously does not violate the Nuclear Non-Proliferation Treaty, but it recalibrates how close a non-nuclear-weapon state can move toward weapons-relevant capabilities while remaining formally compliant. Naval fuel exemptions inherently generate oversight gaps, and once such exemptions are normalized among advanced U.S. allies, the normative barriers around technology that are closely associated with weapons capability diminish. In such contexts, political signaling is equally important. Notably, in both South Korea and Japan, senior political figures have publicly alluded to the possibility of acquiring nuclear weapons under perceived deteriorating security conditions. This tension has only grown more pronounced as regional threats from North Korea and China intensify.

Substantiating this contention, some policymakers in Washington allege that strengthened allied latency — or even limited allied nuclearization — could stabilize deterrence and allow the United States to concentrate strategic resources on balancing China. However, under conditions of a perceived U.S. credibility deficit and worsening regional threats, rather than a stabilizing hedge, managed proliferation can appear as strategic abandonment, making such reasoning inward-looking. It also further risks assuming that normalization can be contained within a small circle of “responsible” allies. And in doing so, the distinction between compliance and capability narrows, as the political cost of moving from latency to acquisition, too, declines. This structural drift does not immediately lead to producing new nuclear-armed states, but it alters expectations about what posture may be viewed as acceptable.

In practice, once near-acquisition is legitimized for some, the normative hierarchy underpinning non-proliferation weakens more broadly. Likewise, if Southeast Asian states pursue civilian nuclear energy amid intensifying great-power competition without adequate regulatory capacity, technical expertise, and safeguards for spent fuel, waste management, and supply chains, comparable governance and proliferation challenges could emerge. This could lead states like Indonesia or Vietnam to eventually reassess their own restraint. In this sense, if a loss of U.S. credibility prompted Japan or South Korea to pursue nuclear weapons — or an increasingly isolationist United States actively encouraged such a shift — it would become far harder to sustain persuasive arguments for continued non-proliferation constraints on Iran or other states in the Middle East.

While North Korean and Chinese capabilities amplify regional nuclear pressures, Southeast Asian states largely view these developments as indirect rather than immediate threats. For most members of the Association of Southeast Asian Nations, the concern lies in the structural consequences of great-power rivalry unfolding in adjacent waters, rather than in an imminent nuclear attack.

Southeast Asia in the Nuclear Crosscurrents

As established, the nuclear balance across East Asia becomes more fluid; Southeast Asia — in strategic effect, no longer remains peripheral. The 1995 Bangkok Treaty establishing the Southeast Asian Nuclear Weapon-Free Zone was designed to insulate the Association of Southeast Asian Nations from major-power nuclear rivalry by prohibiting the development, possession, and deployment of nuclear weapons by member states. However, in the volatile environment today, the primary deadlock lies in Article 2 of the treaty’s protocol, which obliges nuclear-weapon states not to use or threaten to use nuclear weapons within a geographically expansive zone that spans Association of Southeast Asian Nations land, territorial waters, and exclusive economic zones across a vast maritime corridor between the Indian and Pacific Oceans. Nuclear-weapon states, as a result, have often hesitated to endorse these provisions, viewing requirements related to notification and transparency as constraints to their deterrence operations and naval flexibility, particularly as their ballistic missile submarines routinely transit or operate in Association of Southeast Asian Nations-exclusive economic zones. While the United Nations Convention on the Law of the Sea does permit nuclear-submarine transit under “innocent passage” — subject to conditions — and preserves freedom of navigation in exclusive economic zones, the Southeast Asian Nuclear Weapon-Free Zone overlays a broader political commitment for nuclear-weapon states whose deterrence postures rely on routine ballistic missile submarine patrols through these maritime corridors.

Proximity Without Protection: At the Nuclear Margins of the U.S.–Chinese Rivalry

Geopolitical ambitions only compound these tensions further. Maritime disputes in the South China Sea — particularly involving the Philippines, Vietnam, Malaysia, Brunei, and overlapping Indonesian exclusive economic zone claims — blur the practical boundaries of the zone. Ongoing Code of Conduct negotiations, too, underscore that the precise spatial scope of the Southeast Asian Nuclear Weapons Free Zone remains politically contested.

Against this backdrop, China’s signaled willingness to sign the protocol has reportedly been conditioned on interpretive assurances under a memorandum of understanding that the treaty would not undermine its sovereignty claims. Such flexibility allows Beijing to portray itself as a responsible nuclear power while preserving latitude for its own ballistic missile submarine operations in contested waters. At the same time, China’s expanding arsenal and growing civil-nuclear outreach across Southeast Asia embed the Nuclear Weapon-Free Zone within broader strategic competition with the United States, whose freedom of navigation operations challenge Beijing’s claims. The South China Sea has become a frontline of U.S.-Chinese rivalry, with freedom of navigation operations and expanding Chinese military control intensifying strategic friction. By projecting itself as the Association of Southeast Asian Nations’ leading patron, China can deepen political and economic ties that also allow its reinforcement of trade diplomacy, enable it to advance Belt and Road Initiative connectivity across mainland and maritime Southeast Asia, and strengthen its strategic position in the South China Sea.

Additionally, as tensions over Taiwan raise the prospect of major-power conflict — and potential nuclear escalation — Southeast Asian states face growing insecurity alongside a sense of shrinking strategic autonomy. In parallel, safety and transparency concerns remain acute, especially after the 2021 grounding of the USS Connecticut, which highlighted how little regional states are informed about nuclear risks in their own waters. Such opacity feeds broader unease about the long-term implications of nuclear-powered platforms operating in the region. While surveys show many Southeast Asians see the AUKUS security partnership as a counterbalance to China, a significant minority worry it could accelerate arms races and weaken non-proliferation norms.

The consequence is a region that must navigate nuclear-powered deployments not of its own making, amid transparency gaps and uneven political consent.

Despite growing exposure to nuclear-adjacent dynamics from Northeast Asia and major powers, Southeast Asian states largely do not perceive an immediate or existential nuclear threat. The region’s nuclear weapon-free status, coupled with the fact that no proximate nuclear-armed adversary is directing coercive pressure toward Association of Southeast Asian Nations states themselves, means that most governments prioritize strategic visibility, energy security, and conventional deterrence rather than overt nuclear hedging. For instance, Indonesia, Vietnam, and the Philippines still continue to emphasize maritime capacity-building and diplomatic balancing as primary instruments of security.

Yet the absence of acute threat perception does not equate to insulation. Instead, nuclear risk in Southeast Asia emerges structurally: through proximity to third-party nuclear deployments, exposure to naval nuclear propulsion, expanding fuel-cycle capabilities in Northeast Asia, and the gradual normalization of nuclear latency among U.S. allies. In such contexts, proliferation risk remains less demand-driven than contingent, such that it may be kept on the horizon by the slow erosion of distance between compliance and capability, rather than by immediate intent.

The Civil Nuclear Pivot

To add to this, several Southeast Asian states are also beginning to reassess their long-standing aversion to civilian nuclear power, against the backdrop of mounting energy insecurity concerns, climate change commitments, and rising fossil fuel prices. This shift reflects changing energy demands, decarbonization pressures, and the diffusion of civil nuclear technology. In part, this is also driven by advances, particularly in small modular reactors, that have lowered political barriers by promising enhanced safety, flexibility, and reduced upfront costs. Although no Southeast Asian state currently operates a nuclear power plant, five countries — Indonesia, Malaysia, the Philippines, Thailand, and Vietnam — which together account for nearly 90 percent of regional energy demand, have incorporated nuclear power into their long-term national planning. Following these developments, nuclear energy is likely to become operational in parts of Southeast Asia within the next decade.

However, as interest grows, robust safeguards will be essential to prevent diversion of nuclear materials for non-peaceful purposes. While International Atomic Energy Agency safeguards are designed to verify that nuclear material is not misused, particularly through oversight of enrichment and reprocessing, emerging reactor technologies tend to introduce new verification challenges. Some advanced designs involve continuous or online fuel loading, complicating accurate accounting of nuclear inventories. Safeguard frameworks will therefore need adaptation before such technologies are deployed in the region — and globally.

Nuclear energy programs require independent regulators, trained personnel, waste management systems, and secure long-term fuel supply arrangements — things that most states in the region have limited experience with. This gap creates several risks. Weak governance heightens the probability of safety incidents, corruption, or regulatory capture, undermining public trust and international confidence. Further, dependence on foreign suppliers for fuel, technology, and waste management may introduce new strategic dependencies, entangling energy policy with geopolitical alignments. Over time, expanded nuclear infrastructure could also lower technical barriers to nuclear hedging, should regional security conditions deteriorate further.

While Southeast Asia remains far from pursuing nuclear weapons, shifts on its northern periphery are beginning to shape regional perceptions of vulnerability. As debates over deployment, latency, and fuel-cycle autonomy intensify in Japan and South Korea, Southeast Asian policymakers face a subtler question: whether strict nuclear abstention continues to guarantee insulation, or whether it risks strategic marginalization in an environment where nuclear capability — actual or latent — appears to command influence. Political rhetoric also suggests growing unease about strategic visibility. In 2020, Indonesia’s then–maritime affairs and investment minister, Luhut Pandjaitan, had publicly implied that nuclear capability might be the only way for a state to command serious attention from major powers. While rhetorical, such remarks reflect a broader sentiment that strategic relevance increasingly correlates with going nuclear, whether civilian or military. Importantly, however, this shift manifests in a reassessment of safeguards for civilian nuclear energy — once politically taboo across much of Southeast Asia.

Conventional Missiles and Strategic Entanglement

Compounding this renewed interest in civilian nuclear energy, Southeast Asia is also undergoing a steady expansion of long-range conventional strike capabilities. Although these systems remain non-nuclear, their strategic implications extend beyond the conventional domain. In a region already embedded in major-power rivalry, longer-range precision missiles compress decision times, expand target sets, and increase the risks of misperception during crises.

Two structural dynamics drive this trend. First, China’s growing missile arsenal and militarization of contested features in the South China Sea have altered the regional offense-defense balance, incentivizing neighboring states to develop credible counterstrike options. Second, the collapse of the Intermediate-Range Nuclear Forces Treaty removed normative and political constraints on the deployment of ground-launched intermediate-range systems in the Indo-Pacific, normalizing their presence in regional force planning.

For Southeast Asian governments, acquiring long-range strike capabilities is framed as deterrence and strategic hedging rather than arms racing. These systems enhance maritime denial, protect critical sea lanes, and reduce overreliance on external security guarantees. Yet as more states integrate long-range precision fires into their doctrinal postures, the operational environment becomes denser and more complex. The margin for error narrows. This evolution is critical because it unfolds alongside two parallel developments: the increasing presence of nuclear-powered platforms in surrounding waters and the gradual reintroduction of civilian nuclear infrastructure within the region. In such a setting, conventional strikes could intersect with nuclear-adjacent assets or dual-use facilities. A targeting error, misinterpreted launch, or attack on potential infrastructure with perceived strategic value could generate escalation pressures extending beyond Southeast Asia.

Individually, missile modernization, naval nuclear propulsion, and civilian nuclear energy remain legally compliant and strategically defensible. Collectively, however, they erode the structural insulation that once separated Southeast Asia from nuclear dynamics. As technical capacity expands and strategic rivalry intensifies, the distinction between conventional deterrence and nuclear-adjacent risk becomes progressively thinner. The long-term danger, hence, lies in the gradual emergence of tipping points where compliance, exposure, and insecurity converge in a future crisis.

For Southeast Asia, the implications are significant: A global regime designed to prevent horizontal proliferation by policing explicit breaches may prove increasingly ill-suited to managing emerging risks. Over time, such dynamics could normalize nuclear latency as an acceptable feature of international order. Southeast Asia, therefore, is not merely a peripheral arena of great-power rivalry, but a structural inflection point — demonstrating how proliferation risk can intensify even as formal non-proliferation commitments remain intact, and how nuclear hierarchies can be reshaped without explicit weaponization.

Hely Desai is a visiting research fellow at the Henry L. Stimson Center. She holds a masters of philosophy from the University of Cambridge. Her work focuses on nuclear deterrence, defense and security, and the political risks surrounding civilian nuclear energy in Asia.

Image: Navy Office of Legislative Affairs via Wikimedia Commons