Iran’s Nuclear Program And UN Sanctions Reimposition – Analysis

By Paul K. Kerr

UN Security Council Resolution 2231 (2015), which the council adopted on July 20, 2015, implements the Joint Comprehensive Plan of Action (JCPOA) and contains other provisions concerning Iran's nuclear program, Tehran's development of missiles, and arms transfers to and from Iran. In August 2020, the United States invoked the resolution's "snapback" mechanism, which requires the Security Council to reimpose UN sanctions lifted pursuant to Resolution 2231 and the JCPOA. (See CRS Report R40094, Iran's Nuclear Program: Tehran's Compliance with International Obligations, by Paul K. Kerr.) Although that effort failed, France, Germany, and the United Kingdom (UK) (collectively known as the "E3") on August 28, 2025, invoked the snapback mechanism, which resulted in the sanctions' reimposition on September 27, 2025. 

Resolution 2231 stipulates that the council, which has been seized of the "Iranian nuclear issue" since 2006, was to end its consideration of the matter on October 18, 2025. The resolution's snapback mechanism would then have ceased to be operational. The 2025 invocation of snapback not only reimposes previously terminated sanctions but also extends them, and Iran's nuclear program as a subject of Security Council consideration, indefinitely. 

Background: JCPOA 

The JCPOA, finalized in July 2015 by Iran and China, France, Germany, Russia, the United Kingdom, and the United States (collectively known as the P5+1), requires Iran to implement constraints on its uranium enrichment and heavy water nuclear reactor programs, as well as allow the International Atomic Energy Agency (IAEA) to monitor Tehran's compliance with the agreement. These programs have caused international concern because they could produce fissile material for use in nuclear weapons. 

Pursuant to the JCPOA, Tehran received relief from sanctions imposed by the European Union, United Nations, and United States. On the agreement's January 16, 2016, Implementation Day, the Security Council terminated the provisions of seven resolutions: 1696 (2006), 1737 (2006), 1747 (2007), 1803 (2008), 1835 (2008), 1929 (2010), and 2224 (2015). Resolutions 1737 (2006), 1747 (2007), 1803 (2008), and 1929 (2010) all imposed sanctions on Iran.

In May 2018, President Donald Trump issued a memorandum stating that the United States would no longer participate in the JCPOA and would reimpose sanctions that had been suspended pursuant to the agreement. Arguing that subsequent efforts by the remaining JCPOA participants, known as the "P4+1," were inadequate to sustain the agreement's benefits for Iran, Tehran has undertaken some nuclear activities that exceed JCPOA-mandated limits.

Iran's Nuclear Program and Selected JCPOA Provisions 

Beginning in July 2019, the IAEA verified that some of Iran's nuclear activities were exceeding JCPOA-mandated limits; the government has since increased the number of such activities. Tehran has also curtailed IAEA monitoring of Iran's JCPOA commitments, which supplement Tehran's obligations pursuant to its IAEA comprehensive safeguards agreement and the nuclear Nonproliferation Treaty (NPT). (See CRS Report R40094, Iran's Nuclear Program: Tehran's Compliance with International Obligations, by Paul K. Kerr.) 

The NPT, which Iran ratified in 1970, includes prohibitions on obtaining or producing nuclear weapons. Comprehensive safeguards agreements empower the agency to detect the diversion of nuclear material from declared nuclear facilities, as well as to detect undeclared nuclear activities and material. 

Iran also ceased implementing the Additional Protocol to its comprehensive safeguards agreement in February 2021. Such protocols increase the IAEA's ability to investigate undeclared nuclear facilities and activities in nonnuclear-weapon states by increasing the agency's authority to inspect certain nuclear-related facilities and demand information from member states. Pursuant to its JCPOA commitments, Iran is required to implement provisionally its additional protocol; Tehran was to have sought the Iranian parliament's ratification of the protocol no later than October 2023. Iran originally signed such an additional protocol in late 2003, but stopped implementing it in early 2006. 

Moreover, the IAEA no longer conducts JCPOA-mandated monitoring of Iranian compliance with agreement-specific restrictions that supplement Iran's safeguards obligations. Had the JCPOA been fully implemented, most of its nuclear-related restrictions would have expired. At that point, Tehran's nuclear program will be governed indefinitely by Iran's obligations pursuant to the NPT, the government's IAEA comprehensive safeguards agreement and Additional Protocol, and restrictions on specific dual-use "activities, which could contribute to the development of a nuclear explosive device."

UN Security Council Resolution 2231 (2015) and Snapback

In addition to its JCPOA-related provisions, Resolution 2231 imposes other requirements on Iran. For example, the resolution restricted exports of missile-rated items to Iran until October 2023; other restrictions concerning Iranian imports and exports of conventional weapons expired in October 2020. Despite lacking a direct connection to the country's nuclear program, previous arms restrictions, the first of which were imposed by Security Council Resolution 1747, were part of a broad U.S.-led approach of pressuring Iran to comply with relevant council resolutions. (For more on the arms restrictions, see CRS In Focus IF11429, U.N. Ban on Iran Arms Transfers and Sanctions Snapback, by Kenneth Katzman.) 

According to Resolution 2231, a JCPOA participant can, after notifying the Security Council of an issue that the government "believes constitutes significant non- performance of [JCPOA] commitments," trigger an automatic draft resolution keeping sanctions relief in effect. The United States in August 2020 initiated the snapback process, but the P4+1 governments and the Security Council president argued that the United States lacked the right to proceed with snapback. Despite a September 19, 2020, U.S. contention that snapback had reinstated previously terminated sanctions, UN Secretary General António Guterres wrote in a letter the same day that the uncertainty concerning the U.S. initiation of snapback required the Secretary to refrain from proceeding on the matter. 

In February 2021, the Biden Administration reversed the U.S. position on snapback. A February 4, 2025, National Security Presidential Memorandum directed the U.S. Permanent Representative to the UN to "work with key allies to complete the snapback of international sanctions and restrictions on Iran."

As noted, the E3 invoked the snapback mechanism in an August 28, 2025, letter. The Security Council President introduced a draft resolution on September 19 that would have maintained sanctions relief, but the council did not adopt the resolution. 

China and Russia subsequently introduced a resolution on September 26 that would have effectively extended the end of Security Council consideration of the "Iranian nuclear issue" until April 18, 2026, with "a possibility for a further extension." The council did not adopt the resolution. The conclusion of the snapback process resulted in the sanctions' reimposition on September 27, 2025. The same day, Secretary of State Marco Rubio described the E3 action as "an act of decisive global leadership."

An October 18, 2025, letter to the Security Council from China, Iran, and Russia argues that the E3 lacks standing to invoke the snapback mechanism because the three governments had "ceased to perform" their JCPOA and Resolution 2231 commitments. The E3 also failed to "exhaust the procedures" of a dispute resolution mechanism contained in the JCPOA, according to the letter, which also stipulates that both Resolution 2231's provisions and the council's "consideration of the Iranian nuclear issue" have ended. The dispute concerning the resolution's status continued during a December 23 Security Council meeting. 

In addition to reimposing sanctions, snapback has ended the process by which the Security Council was to cease in 2025 its consideration of the Iranian nuclear issue. The council adopted all of the resolutions that imposed sanctions on Iran, as well as Resolution 2231, under Article 41 of Chapter VII of the UN Charter. This article enables the Security Council to adopt "measures not involving the use of armed force," including sanctions, "to give effect to its decisions" concerning "threats to the peace, breaches of the peace, and acts of aggression." Since adopting Resolution 1737 in 2006, the council has been considering the Iranian nuclear issue pursuant to Article 41.

Possible Iranian Responses

Reacting to the invocation of snapback, Iranian Foreign Minister Abbas Araghchi stated on September 30 that "Iran's Supreme National Security Council will assess the situation and ultimately adopt 'the right and well-calculated decisions' in line with national interests."

Iran has cited JCPOA Paragraph 36 as grounds for Tehran's decision to end all JCPOA-mandated transparency measures beyond the government's comprehensive safeguards agreement. If Iran were to end its JCPOA participation entirely, the government would be bound only by its comprehensive safeguards agreement, which is of indefinite duration. Iran would not be bound by its Additional Protocol.

In such an event, the IAEA would retain its monitoring and inspection authority pursuant to Iran's comprehensive safeguards agreement, but the scope of this authority would be narrower. For example, the agency would lose JCPOA authority to monitor certain Iranian facilities that do not contain nuclear material but are associated with the government's enrichment program. The IAEA would also retain its authority to verify the absence of undeclared nuclear material and activities, but the agency would, absent Iran's adherence to Tehran's additional protocol, have fewer means to do so.

Moreover, Tehran would not be bound by the JCPOA constraints on the government's enrichment program, although Iran would remain bound by its NPT obligations. Significant expansion of Tehran's enrichment program has decreased the amount of time necessary for Iran to produce enough fissile material for use in a nuclear weapon (see CRS In Focus IF12106, Iran and Nuclear Weapons Production, by Paul K. Kerr).

Prior to the JCPOA, Iran was improving its ability to produce fissile material, despite UN and other sanctions' evident success in slowing the nuclear program. At the time, knowledgeable IAEA and U.S. officials observed that IAEA safeguards on Iran's declared nuclear facilities would likely have detected an Iranian attempt to use them for producing nuclear weapons. (For more information, see CRS Report RL34544, Iran's Nuclear Program: Status, by Paul K. Kerr.) Nevertheless, Iran's continuing nuclear program concerned many governments; Israel and the United States both attacked Iranian nuclear facilities in June 2025.

Iranian officials have indicated that the government might withdraw from the NPT in response to snapback. In this case, Tehran would not be bound by its comprehensive safeguards agreement or its treaty obligations. These Iranian officials, reiterating a long-standing government position, have stated that Tehran would still refrain from producing nuclear weapons.

• About the author: Paul K. Kerr, Specialist in Nonproliferation
• Source: This article was published by the Congressional Research Service (CRS).