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Germany, France and the U.K. are expected to trigger the reimposition of U.N. sanctions on Iran, according to three European officials who spoke with CNN on Wednesday.

The so-called “snapback” mechanism, which is part of the 2015 Iran nuclear deal, is expected to be put into motion as soon as Thursday.

It takes 30 days for the snapback mechanism to go through, so the Europeans are setting a deadline for diplomacy. European leaders hope Tehran will use the time to reengage with the world in serious negotiations, open its doors and facilities for international inspectors, and take actions to show it is working toward coming into compliance with its nuclear obligations.

Iran has threatened harsh retaliation against a return of sanctions, however, which could further fan instability in the Middle East, just as the conflict that erupted last month has started to subside.

Snapback Mechanism Is Winding Down

The Joint Comprehensive Plan of Action (JCPOA) from 2015 has a snapback provision, in which members can trigger a return of UN sanctions if they think Iran is in violation of the agreement.

The members that can trigger the snapback – France, Germany, the U.K. and the U.S. – have authority to do so until October, and the Europeans are eager to act before the Aug. 22 return of those members to the U.N. Security Council.

Iran has expanded its nuclear program beyond the boundaries of the JCPOA since former President Donald Trump withdrew from the agreement in 2018. Tehran says its nuclear program is purely peaceful, but inspectors and experts are warning it is on track to amass enough nuclear material, and to enrich it to a high enough level, to make a weapon if it so chooses.

“Going back to the original JCPOA would be almost impossible,” Rafael Grossi, the head of the International Atomic Energy Agency, said Wednesday.

U.S. Secretary of State Marco Rubio, who spoke with his European counterparts throughout the week in preparation for the decision, said Wednesday that the snapback mechanism is “a very powerful piece of leverage on the Iranian regime.”

Inspectors have been on the ground in Iran after the nation’s parliament last month voted to cut ties with the IAEA. But the IAEA has since moved its inspectors back into place, Grossi confirmed, and he noted that inspectors are now at the Bushehr nuclear power plant as of Wednesday.

“The Agency’s inspectors are already on the ground in Iran,” he tweeted. “Today we are inspecting Bushehr. We are continuing the conversation so that we can go to all places, including the facilities that have been attacked.”

The IAEA inspectors have the ability to go to any of the sites on any timeline because its safeguards agreement is rooted in the Nuclear Non-Proliferation Treaty (NPT), which Iran is a signatory to.

Iran is reportedly considering withdrawal from the NPT as one of its options if snapback is triggered.

Iranian Foreign Minister Abbas Araghchi said the Bushehr inspectors were monitoring the replacement of fuel there following a decision by Iran’s Supreme National Security Council. He denied there was any wider understanding for “new cooperation.”

Aftermath from Recent Conflict

Iran’s nuclear program has been a major source of tension since Israel attacked Iran’s nuclear facilities in June, which started a 12-day conflict. Iran then retaliated with missile and drone attacks on Israeli cities and U.S. forces also joined the conflict in the final days, attacking three Iranian sites.

The IAEA said in July that it had withdrawn its inspectors from Iran, saying it would be unable to monitor the country’s nuclear program while the war continued.

Satellite images later showed damaged entrances at the Isfahan Nuclear Technology Research Center, and the IAEA said Iran was continuing to take prohibited steps on its nuclear program, including enriching uranium to 60%, which is weapons-grade level.

Tehran later accused the agency of giving Israel an excuse to strike by publicizing Iran’s non-compliance with IAEA safeguard rules.

Iran Divided on Response

Iran has come under fire at home for allowing the IAEA inspectors back into the country after the parliament passed the legislation cutting ties with the agency.

Parliamentary member Kamran Ghazanfari, a member of the Supreme National Security Council that was at the center of the dispute, spoke out against the return of IAEA inspectors on Wednesday. He called comments from Speaker Mohammad Bagher Ghalibaf in support of limited inspections an “explicit violation” of the law that the parliament passed to suspend ties with the agency.

The parliament passed the legislation after the June conflict ended, saying it would protect Iran from foreign invasion and what it sees as the IAEA’s biased reporting on Iran’s nuclear program.