U.S. efforts since early 2021 to restore the multilateral deal limiting Iran's nuclear program have been unsuccessful, and recent public statements by U.S. and European officials suggest that the attempt has de facto been abandoned. None of the parties, which include China, France, Germany, Russia, and the United Kingdom, have yet taken the formal step that would end the deal, however: triggering the "snapback" mechanism of U.N. Security Council resolution 2231, which underpins the accord.

Snapback involves the re-imposition of Security Council sanctions from earlier resolutions on Iran in the event of "significant non-performance" of Iran's commitments under the accord, formally called the Joint Comprehensive Plan of Action (JCPOA). Snapback can be triggered by any JCPOA participant state, and previous U.N. sanctions would take effect automatically 30 days thereafter, unless the Security Council votes to continue lifting sanctions.^[i]

The United States attempted to initiate snapback in 2020, but its standing to do so was rebuffed by the Security Council due to Washington's exit from the JCPOA in 2018.^[ii] France, Germany, and the United Kingdom (the "E3") retain the standing to trigger the mechanism but have been reluctant to do so, preferring a negotiated return of the United States and Iran to compliance with the JCPOA. Yet the halt of negotiations and Iran's actions beyond the nuclear issue have increased the likelihood that their forbearance will expire before resolution 2231 does in 2025.

Triggering snapback sooner would provide the E3, the United States, and like-minded countries with a set of tools that could be immediately put to use in countering the wider proliferation problem posed by Iran, including Tehran's supply of weapons to Russia for use against Ukraine. On balance, it is worth the risks that formally signaling the end of the JCPOA would bring. Short of initiating snapback, the E3 at a minimum should not allow remaining European nonproliferation sanctions on Iran to sunset on schedule in October, and instead reimpose those sanctions that the JCPOA had suspended.

The Logic of Snapback

That Iran is not performing its JCPOA commitments is not in doubt. Its accumulation of uranium enriched up to 60 percent purity, deployment of advanced centrifuges, and rejection of International Atomic Energy Agency (IAEA) monitoring mandated by the JCPOA provide ample justification for one of the E3 to trigger snapback.

Outside the scope of the JCPOA, Iran has supplied Russia with drones to use against Ukraine, transferred missiles and arms to the Houthis, refused to cooperate with the IAEA's investigation into the presence of uranium at undeclared sites in Iran, and violently repressed popular protests. These actions have dimmed European leaders' perception of Iran as a constructive negotiating partner. They have also reduced the likelihood that triggering the snapback mechanism would be controversial among EU member states.

In the meantime, the restrictions contained in resolution 2231 are dwindling. Limitations on Iran's arms transfers expired in 2020, and restrictions on drone- and missile-related transfers will expire in October along with the resolution's list of entities still subject to an asset freeze. In 2025, the two remaining provisions will also expire: restrictions on nuclear-related transfers and the snapback mechanism itself. In addition, the JCPOA stipulates that the European Union will lift proliferation-related sanctions by October 2023. The accord's own restrictions on Iran's nuclear program begin to sunset in early 2024, with the majority being lifted by the start of 2031.

Several forces are therefore pushing European leaders toward triggering snapback. There is a desire to punish Iran for its bad behavior, and to do so quickly, before existing restrictions expire. Domestic political pressure, both within Europe and, indirectly, from the United States, may also strengthen the impetus to act.

Once it is triggered, however, snapback would unleash a multitude of consequences, both direct and indirect. The direct consequences arising from restored U.N. sanctions would yield mixed results and provide the most benefit in areas outside the nuclear issue, such as Iranian arms transfers. The indirect consequences of snapback, including Iran's own reaction to it, are less certain but could vastly overshadow the direct ones.

The Direct Consequences of Snapback

Snapback would restore the provisions of resolutions 1696, 1737, 1747, 1803, 1835, and 1929 and nullify the sunset clauses of resolution 2231. Although on paper such a reversion would represent a dramatic shift, in practice the consequences would be more limited. This is largely because China and Russia may reject the legitimacy of the move and would likely refuse to enforce renewed sanctions.

Shipping and Arms Transfers

Snapback would restore resolution 1929's asset freeze against Islamic Republic of Iran Shipping Lines (IRISL), its subsidiaries, and anyone acting on their behalf. Additionally, resolution 1929 calls upon all states to inspect any cargo passing through their ports and airports to and from Iran if they have reasonable grounds to believe such shipments contain prohibited items, and it enables them to inspect ships on the high seas with the consent of the vessel's flag state if there are reasonable grounds to believe that vessel is transporting any prohibited items. Finally, it requires states to forbid "bunkering services" (such as refueling) to vessels that they believe are carrying those prohibited items, with some exceptions.

What constitutes a prohibited item would expand under a snapback scenario. Snapback would revive the general arms embargo against Iran, meaning any transfer of major conventional weapon systems, parts, and training to Iran would be forbidden. Moreover, Iran would be banned from transferring any weaponry whatsoever to another state. The transfer of many nuclear and missile-related items would also be expressly banned. These include, with some exceptions, any items that would contribute to Iran's nuclear enrichment-, reprocessing-, or heavy water-related activities and almost all items on the Missile Technology Control Regime list.

The economic impact of such changes may be small. IRISL is already the subject of U.S. secondary sanctions, and these sanctions have substantially deterred Western and multinational companies from doing business with it. Companies that have not been deterred by U.S. sanctions – particularly firms in China, with which Iran conducts most of its trade – may not be fazed by renewed Security Council prohibitions.

On the other hand, the restored provisions would have counterproliferation utility, particularly in regard to conventional arms transfers. For example, governments and firms in countries on the Caspian Sea, in Africa, in Latin America, and elsewhere in Asia may become more wary of IRISL-affiliated vessels, and more thorough in their due diligence – thus complicating Iranian smuggling efforts. Additionally, the United States and its partners would have a broader legal basis for stopping and searching ships traveling to and from Iran and seizing illicit cargo.

Targeted Sanctions

Snapback would impose targeted U.N. sanctions against some 78 organizations and 43 individuals, encompassing all entities currently on the 2231 List plus the aforementioned shipping companies, the Atomic Energy Organization of Iran, several Iranian nuclear facilities, and more than a dozen officials who have worked on the nuclear program.^[iii] All these entities would be subject to asset freeze measures which are otherwise set to expire in October, and the travel ban on listed individuals that expired in 2020 would be reinstated.

Yet the effect of these targeted sanctions may be minor, for several reasons. First, the bulk of the entities (61 organizations and 23 individuals) are already subject to the 2231 List's asset freeze. Second, the United States has sanctioned nearly half of the 36 entities that were de-listed in 2015, so those entities' access to foreign funds are heavily restricted regardless of the status of the U.N. sanctions. Finally, the U.N. designations are woefully out of date; many of the sanctioned officials have moved on to new positions since the designations were last updated, and other officials now fill the relevant posts.

The return of resolution 1929 would also bring back an admonishment for states to prevent Iranian banks from setting up operations in their territories, and their own banks from setting up operations in Iranian territory, if they have grounds to believe such activities could support Iranian proliferation. This could prompt European countries in particular to close branches of the few Iranian banks operating in their territories, such as Bank Saderat Iran, though the limited scale of those operations means that the counterproliferation impact – of denying Iran an avenue into Europe's financial system – would be more meaningful than the economic impact.

Nuclear and Missile Programs

The return of the six prior resolutions would represent a major shift in the international legal status of Iran's nuclear and ballistic missile activities. On the nuclear side, the demands of resolution 1737 would come back into force. Specifically, Iran would be required to immediately suspend all enrichment and reprocessing activities, suspend all work on heavy water-related projects (except the conversion of the Arak reactor), and ratify and implement the Additional Protocol to its Comprehensive Safeguards Agreement with the IAEA.

On the missile side, the language of resolution 1929 that Iran "shall not undertake any activity related to ballistic missiles capable of delivering nuclear weapons" would return. This would be a stronger prohibition compared to that of resolution 2231, which only "calls upon" Iran not to conduct any activity related specifically to those ballistic missiles that are "designed to be capable" of carrying nuclear weapons. Moreover, snapback would prevent resolution 2231's limitation from sunsetting in October 2023.

Of course, Iran did not fully heed these restrictions at the time they were adopted and would not heed them today.

Monitoring Measures

The triggering of snapback would revive useful monitoring bodies, including a committee (commonly called the 1737 Committee) to monitor implementation of the six resolutions and issue regular reports on their implementation. Snapback would also provide for the establishment of a panel of experts to assist the committee. Before the JCPOA, the panel was charged with carrying out investigations of alleged non-compliance with Security Council resolutions and outreach to support sanctions implementation and enforcement.

Because the committee and the panel would consist of all members of the U.N. Security Council, Russia and China would be empowered to obstruct their work. For example, one of the committee's main purposes is to help inform the adoption of new Security Council resolutions and targeted sanctions, but Russia and China would almost certainly veto the adoption of any new resolution against Iran and block additional targeted sanctions against individuals and entities.

The panel of experts would be similarly hindered and might be prevented from reconstituting at all. Although resolution 1929 authorized the U.N. Secretary General in 2010 to establish a panel of experts for an initial period of one year, extending the panel's mandate for additional one-year terms requires Security Council sign-off. Russia or China could veto a resolution to renew the panel's mandate.

The Indirect Consequences of Snapback

Triggering the snapback mechanism would not happen in a vacuum, and the reactions and subsequent moves of several actors are likely to affect the ultimate outcome. Such second- and third-order effects are unpredictable, but a few possibilities can be anticipated.

Expansion of European Sanctions

A decision to trigger snapback would almost certainly result in the re-imposition of European sanctions against Iran that were in force before JCPOA.^[iv] These included sanctions on Iran's banking, insurance, oil, gas, and shipping sectors, and targeted designations of entities such as the Central Bank of Iran, the National Iranian Oil Company, and the National Iranian Tanker Company. These measures would increase the economic impact of EU sanctions.

The European Union and the United Kingdom would also be free to impose additional restrictive measures against Iran's nuclear program, using regulations that are currently unavailable because of constraints imposed by the JCPOA.^[v]

More broadly, the decision to close the book on the JCPOA would likely presage a shift to a more forward-leaning European sanctions policy. The European Union would be more likely to sanction activities and entities related to Iran's drone and missile industries, against which Europe has taken almost no public action since the JCPOA's implementation.

Risk of Escalatory Reactions

Triggering snapback would signal that diplomatic efforts to resolve the nuclear issue are over, at least for the near-term. As a result, there would no longer be an incentive for Iran to exhibit the minimum restraint necessary to preserve the JCPOA diplomatic track as a policy option. This, and the desire to retaliate for the additional sanctions that would be imposed, may provide Iran a pretext to take provocative steps in its nuclear program. Such steps could include enriching uranium to weapon-grade, further limiting IAEA monitoring, withdrawing from the Nuclear Nonproliferation Treaty (NPT), or carrying out clandestine uranium enrichment or "weaponization" work to produce a nuclear warhead. Iran could also step up its aggressive actions in the Persian Gulf or elsewhere in the Middle East.

Such an Iranian reaction could prompt a counter-reaction by Iran's adversaries, particularly Israel, which may expand covert and military actions against Iran. A series of tit-for-tat kinetic responses could escalate, which in its worst cases could result in an Iranian dash to a nuclear weapon and/or a military crisis or regional war. The United States could also get drawn into a conflict at several points along the escalation ladder.

Yet these risks are also present if the snapback mechanism is not triggered. Iran has already used the period of negotiations to make substantial technical progress toward a nuclear weapon and a long-range delivery system, and failure to utilize resolution 2231's punitive measure while the rest of its restrictions wither under sunset clauses may be interpreted by Iran as an invitation for even bolder advances. A sense of impunity could also embolden Iran to behave more aggressively in its region, whereas a sense that the West is unwilling to take action against Iran could lead Iran's regional adversaries to conclude that they must act unilaterally.

The primary risk, therefore, is that snapback precipitates a confrontation that may already be unfolding. The timing of such a confrontation, however, is important: a crisis in the Persian Gulf would disrupt energy supplies at a time when Europe already faces an energy shortage caused by the Russian invasion of Ukraine.

Conclusion and Recommendation

Triggering the snapback mechanism would not halt Iran's progress toward a nuclear weapon, nor would it on its own have a devastating effect on Iran's economy. Maintaining the JCPOA would leave Iran a face-saving way to accept renewed monitoring and restrictions on its nuclear program, should some change in Iran's international or domestic situation convince the Iranian government to do so. It would also leave the United States and its partners with a ready diplomatic framework if this change occurs.

But the nuclear program is not the only proliferation problem posed by Iran. Iran's transfer of drones, missiles, and other arms to nonstate actors continues to destabilize the Middle East, and by supplying drones – and potentially ballistic missiles – to Russia, Iran is exacerbating the biggest current challenge to multilateralism and a stable world order, which underpin the nuclear nonproliferation regime.

Initiating snapback would give Europe, the United States, and other countries another set of tools to confront the pressing problem of Iranian arms transfers. Expanded international legal authority to inspect cargos would increase the likelihood of interdiction and raise the cost to Iran of smuggling. Sanctions on IRISL and denial of bunkering services to suspect ships would make it more difficult for Iran to transport weapons using its own vessels.

The convergence of Europe's Iran sanctions regime with the United States' would also have value. It would enable more effective coordination to cut off Iranian illicit financial and procurement activities in Europe and beyond, and provide a sanctions benchmark for other countries.

These benefits may be incremental, but would, over time, constrain the quality and quantity of arms, including missiles and drones, that Iran is able to develop and transfer abroad. And while snapback carries risks of escalation that would be difficult to manage, those dangers are nonetheless present, and their likelihood of being realized depends on calculations in Tehran and elsewhere that are influenced by factors beyond the JCPOA negotiations.

The situation at present therefore argues in favor of taking the initiative and triggering snapback – perhaps in connection with the next meeting of the IAEA's Board of Governors in March. This would allow the United States and its partners to immediately make use of the expanded counterproliferation tools provided for in previous Security Council resolutions and to begin accumulating their effects. Doing so would also raise the floor, globally, for punitive action against Iran and could increase Iran's diplomatic isolation.

At a minimum, the E3 should not allow remaining European nonproliferation sanctions on Iran to sunset on schedule in October, and should instead reimpose sanctions that the JCPOA had suspended – essentially taking themselves out of compliance with the accord, as Iran has done, without declaring the JCPOA formally defunct. Doing so would enable European and U.S. sanctions convergence, but forego the benefit of worldwide restrictions on Iranian shipping that snapback would bring.

Inaction over the past several months has not served the E3 well either in regard to Iran's nuclear program or the broader nonproliferation picture. If the nuclear problem is intractable for now, then it is time for Europe to set the JCPOA aside and act where it can.