On June 21, the United States conducted airstrikes on three nuclear sites in Iran—Fordow, Natanz, and Esfahan—marking the first direct U.S. military attack on Iran’s nuclear program. The strikes bring the United States directly into the Israel-Iran War that began on June 13 with Israeli attacks against Iranian nuclear and military infrastructure, as well as top officials and scientists. The strikes also risk a dramatic escalation, potentially expanding into a much broader conflict. In a White House address, President Donald Trump described the U.S. operation as “highly successful,” claiming the targeted sites were “totally and completely obliterated.” At the time of this writing, no independent battle damage assessment (BDA) has been released. Chairman of the Joint Chiefs of Staff General Dan Caine stated, “I think BDA is still pending, and it would be way too early for me to comment on what may or may not still be there.” Iran has condemned the strikes as a violation of international law and requested an emergency U.N. Security Council session, threatening “everlasting consequences.”
These developments raise urgent questions about the risks of regional escalation, the legality of unilateral military action, and the long-term implications for the global nonproliferation regime. The following analysis aims to assist policymakers, lawmakers, journalists, and the public assess the implications of this moment. For further expert commentary, see other installments in Just Security’s collection on the Israel-Iran conflict.
Iran’s Retaliatory Options
Iran now faces a range of constrained but potentially destabilizing choices. Iranian leaders likely will try to reassert deterrence through a show of continued strength, while avoiding actions that could trigger full-scale war with the United States. Setting aside legal considerations, the below options are not mutually exclusive and carry varying levels of risk in terms of conflict escalation and potential blowback to Iran:
Missile and Drone Strikes. Iran maintains a diverse and advanced missile stockpile, with some capable of targeting the United States and its allies, although the Israeli government claims to have destroyed half of Iran’s missile launchers since June 13. Tehran may opt for a calibrated strike—similar to its 2020 missile attack on Al-Asad Airbase in Iraq, which houses U.S. and allied forces, following the U.S. drone strike that killed Iranian general Qassem Soleimani in Iraq. (That strike resulted in over 100 U.S. troops suffering traumatic brain injuries.) Such a strike could demonstrate resolve while aiming to stay below the threshold of major escalation, but it may not be viewed within Iranian leadership as a sufficient response to the U.S. use of force against Iran.
Proxy and Terrorist Attacks. Iran may activate regional proxies such as Hezbollah in Lebanon, Shia militias in Iraq and Syria, or the Houthis in Yemen. These groups could target U.S. personnel, military installations, or allied interests in the region. The Houthis have already threatened to target U.S. naval vessels in the Red Sea in response to the U.S. strikes. A Hezbollah spokesperson, by contrast, indicated the group has no immediate plans to retaliate following the U.S. strikes.
Even if these groups do join the fighting, Iran’s most capable regional proxies—Hezbollah and Hamas—have suffered major setbacks since the Israeli response to the Hamas-led attacks of Oct. 7, 2023. Israeli officials estimate that Hezbollah maintains only some 20 percent of the missiles and rockets it had before the war. Dozens of senior Hezbollah commanders, including the longtime leader Hassan Nasrallah, have been killed in targeted Israeli strikes. Hamas, meanwhile, has seen much of its leadership killed or displaced, and its military infrastructure in Gaza severely degraded by sustained Israeli operations.
Tehran may also turn to transnational terrorism. The direct use of force against Iran could prompt attacks beyond the region. Hezbollah-linked operatives and Iranian sleeper cells may pose a potential threat to Israeli, European, or U.S. interests. Iran has demonstrated the intent and capacity to orchestrate extraterritorial attacks, including a foiled 2011 attempt to assassinate the Saudi ambassador in Washington, DC; a 2022 murder-for-hire plot targeting Iranian-American journalist Masih Alinejad in New York City; alleged plots against former National Security Advisor John Bolton and former Secretary of State Mike Pompeo; and reported threats against Trump in 2024.
Maritime Disruption. Iran could attempt to disrupt maritime traffic in the Strait of Hormuz through mining, drone activity, or harassing commercial and military vessels. Such action would threaten global energy markets and signal Tehran’s willingness to retaliate, but also pose a high risk of direct confrontation with U.S. and allied forces that could threaten regime survival. Such a move also risks angering China—the largest importer of Iranian oil—whose economy is dependent on energy transported through the Strait, and has so far remained relatively neutral in the conflict.
Cyber Operations. Cyber retaliation remains a likely and strategically flexible option. Iran has previously targeted critical infrastructure through cyberattacks and has intensified such operations amid ongoing conflict with Israel. Iranian malicious cyber activity reportedly surged by more than 700 percent since June 13.
A cyber response could allow Iran to impose costs while retaining plausible deniability. Potential targets include energy infrastructure, telecommunications systems, financial networks, and other critical infrastructure within the United States and abroad. U.S. companies are on high alert, but defensive gaps remain—particularly in light of the Trump administration’s recent staff reductions and proposed additional budget cuts at the U.S. Cybersecurity and Infrastructure Security Agency.
Cyber escalation is inherently unpredictable. Even without deliberate targeting, malicious code can propagate widely, as seen in the unintended global spread of Stuxnet—an alleged U.S.-Israel cyberweapon designed to disrupt Iran’s centrifuges that ultimately infected companies based in the United States.
Withdrawal from the Nuclear Non-Proliferation Treaty (NPT). Iran may choose to withdraw from the NPT and reconstitute its nuclear program outside international oversight. (The treaty obligates non-nuclear-weapon States to forgo the development or acquisition of nuclear weapons, while allowing access to peaceful nuclear technology under IAEA safeguards, among other constraints.) While this would carry significant diplomatic and economic consequences, it could serve as a form of strategic signaling and raise the specter of a nuclear breakout (see further discussion on potential NPT withdrawal below.)
Legal Status of the Strikes
From a domestic legal perspective, the U.S. Constitution vests the power to declare war in Congress. The June 21 strikes were carried out without congressional authorization, and the Trump administration has not invoked any existing statutory basis—such as the 2001 or 2002 Authorizations for the Use of Military Force (AUMFs)—to justify the operation. As Brian Egan and one of us (Tess Bridgeman) have explained, neither of those two AUMFs authorize war against Iran; moreover, direct strikes against Iran on its territory with the obvious threat of regional escalation almost certainly rise to the level of “war in the constitutional sense,” such that the President could not rely on Article II authority alone but would need congressional authorization.
The War Powers Resolution requires the president to notify Congress within 48 hours of hostilities and requires withdrawal from otherwise unauthorized military operations after 60 days unless Congress provides authorization. Congress could also try to pass a bill under the War Powers Resolution to require withdrawal immediately (a few such bills have already been introduced), but it would have to overcome a potential presidential veto to be enacted. Regardless, the absence of any legislative authorization in such a consequential use of force raises serious concerns about democratic accountability and the erosion of Congress’ constitutional role.
From an international legal perspective, the U.N. Charter prohibits the use of force against the territorial integrity of another State under Article 2(4), except in narrow cases of self-defense under Article 51 or with U.N. Security Council authorization. The United States has not yet publicly presented evidence of an imminent armed attack that would justify self-defense under Article 51.
The United States also has not cited a formal request for collective self-defense from Israel, although Israel has publicly called on the United States to do so. At a press conference following the U.S. strikes, Secretary of Defense Pete Hegseth said, “the president authorized a precision operation to neutralize the threats to our national interests posed by the Iranian nuclear program and [in support of] the collective self-defense of our troops and our ally, Israel.” Any formal invocation of collective self-defense, however, would merit close scrutiny, considering the legality of Israel’s military intervention is subject to debate (see here and here). In the absence of either a self-defense or collective self-defense justification, the strikes may be viewed as preventive, placing them on uncertain legal footing at best.
Even if the United States does present such a case, any use of force under international law must meet the requirements of necessity and proportionality. The United States has not yet explained how targeting multiple nuclear facilities within a sovereign country—absent an imminent threat originating from those sites—comports with these legal requirements. Importantly, the imminent threat would need to encompass not only Iran’s potential to acquire a nuclear weapon soon but also an intention to use it. As Adil Haque recently wrote, “Any notion that Iran intends to trigger mutually assured destruction is delusional and cannot provide a rational basis for the use of force under international law.”
One key question is if President Trump is correct that “Iran’s key nuclear enrichment facilities have been completely and totally obliterated,” then the U.S. and Israeli operations would have achieved their objective. In such a case, the legal basis for the continued use of force would no longer be necessary or proportionate.
(Note: we do not address here the rules of armed conflict that apply to attacks on nuclear facilities.)
Implications for the Nonproliferation Regime
On June 12, the International Atomic Energy Agency’s Board of Governors found Iran in “non-compliance” with its safeguards obligations, marking the second such finding in two decades. Notably, Iran was in compliance with its NPT obligations and additional monitoring measures under the 2015 Joint Comprehensive Plan of Action (JCPOA) until the United States withdrew from the deal in 2018. However, Iran still remains a party to the NPT, which legally requires it to permit IAEA inspections of its declared nuclear facilities.
The U.S. strikes place IAEA verification and monitoring at serious risk and may have significant consequences for the credibility of the NPT, which is regarded as the cornerstone of the global nuclear nonproliferation regime:
- Undermining the Inspection Process. While the IAEA has formally declared Iran to be in breach of its nonproliferation obligations and has decreased international access since the U.S. JCPOA withdrawal, attacking a State under IAEA monitoring, particularly before exhausting diplomatic options, may still be perceived as punishing transparency and cooperation. This risks discouraging other States from voluntarily submitting to IAEA safeguards out of concern that openness could increase their vulnerability to military action.
- Risk of NPT Withdrawal. Iran could choose to invoke Article X of the NPT and withdraw from the treaty, following North Korea’s path in 2003. Taking this step could allow Iran to reconstitute and expand its nuclear program outside most legal or technical constraints.
- Precedent for Preventive Force. The strikes may set a corrosive precedent for the use of force against nuclear infrastructure in the absence of clear evidence of an imminent threat. This challenges the core logic of the NPT—that proliferation concerns should be addressed through verification and diplomacy, rather than unilateral military action.
More broadly, these developments could reinforce a perception that non-nuclear-weapon States remain vulnerable to coercion or attack, while nuclear-weapon States may act with impunity. Over time, such perceptions may erode trust in the nonproliferation regime and incentivize other States to pursue nuclear capabilities as a means of deterrence.
On the other hand, an argument sometimes raised is that the use of force can reinforce the nonproliferation regime by deterring States from developing nuclear weapons or violating their legal obligations under the NPT. However, this line of argument would be widely understood by foreign capitals as a rejection of the diplomatic choices in constructing the NPT itself. It is difficult to see how such an approach and the NPT could both remain viable.
