Germany, France and the United Kingdom plan to trigger the return of United Nations sanctions on Iran, three European officials told CNN on Wednesday. The so-called “snapback” mechanism built into the 2015 Iran nuclear deal could be set in motion as early as Thursday.

The process takes 30 days to complete, leaving a narrow window for diplomacy. European leaders hope that Tehran will use that time to reengage in meaningful negotiations, open its facilities to international inspectors and take steps to comply with its nuclear obligations.

Iran, meanwhile, has threatened retaliation of unspecified severity if sanctions are reimposed, and the move carries the potential to further destabilize a region already rocked by recent conflict.

The snapback provision in the 2015 Joint Comprehensive Plan of Action (JCPOA) allows members to restore UN sanctions on Iran if it violates the agreement. The authority will expire in October, according to the Associated Press, meaning there is urgency to the European plan.

Iran has ramped up its nuclear program far beyond JCPOA limits since former President Donald Trump withdrew from the agreement. Tehran maintains its program is peaceful, but its capabilities are growing closer to weapons-grade, alarming inspectors and analysts.

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

U.S. Secretary of State Marco Rubio, who spoke with his European counterparts on the issue this week, called the snapback “a very powerful piece of leverage on the Iranian regime.”

Inspectors Return as Climate Gets Testy

Iranian parliament passed legislation to halt cooperation with international inspectors at nuclear facilities. But Grossi announced that IAEA teams have returned, and were at the Bushehr nuclear power plant on Wednesday.

“The inspectors are in Bushehr today,“ he said at a news conference in Washington. “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’s safeguards stem from the Nuclear Non-Proliferation Treaty (NPT), of which Iran is still a signatory. The Associated Press reported Wednesday that Iran’s options if sanctions return include withdrawal from the NPT.

Iranian Foreign Minister Abbas Araghchi said the inspectors were on the ground to monitor fuel replacement at Bushehr, based on a decision from the Supreme National Security Council. He later said there was no “new agreement” for “new cooperation” with the IAEA.

Trouble Comes From Recent Conflict

Israeli forces struck Iran’s nuclear facilities in June, igniting a 12-day conflict. Iranian retaliatory attacks targeted Israeli cities, and U.S. forces joined in the final days, striking three Iranian sites.

The IAEA pulled its inspectors in July, saying that the wartime environment had made monitoring impossible. Satellite images showed damage to the entrances of Iran’s Isfahan Nuclear Technology Research Center.

Tehran has accused the agency of giving Israel a pretext for its strikes by publicizing Iranian non-compliance with safeguard rules.

The decision to allow IAEA inspectors at certain facilities has already attracted criticism at home. Parliamentary member Kamran Ghazanfari lashed out in a statement against comments by Speaker Mohammad Bagher Ghalibaf supporting “partial and conditional” inspections. Ghazanfari called Ghalibaf’s comments an “explicit violation” of the laws the parliament passed in July suspending cooperation with the agency.

Iran’s parliament had passed the legislation in the wake of the June conflict, which it framed as a defense against foreign aggression and IAEA reporting perceived to be biased against Iran.

European negotiators held talks with Iranian representatives in Geneva on Tuesday in a last-minute bid to avoid sanctions. But sources told CNN little progress was made.

Witkoff had been engaged in diplomatic outreach prior to the conflict to build a new nuclear agreement, but those talks have long since collapsed with the fighting.

Grossi remains cautiously optimistic that the next month could see some cooling of tensions. “Don’t forget that there is still time, even if there is the triggering thing, there is a month, and many things could happen,” he said.

For now, Iran is facing pressure from both the West and from within its own political system. With the snapback mechanism set to expire in October, the coming weeks could determine whether diplomacy survives, or whether sanctions and confrontation define the next chapter of the nation’s nuclear saga.