Germany, France and the United Kingdom are expected to announce a decision to reinstate U.N. sanctions on Iran, three European officials said Wednesday. If triggered as early as Thursday, the so-called “snapback” provision in the 2015 Iran nuclear deal takes 30 days to complete.

European leaders hope the process, which could still be averted through diplomacy, will open a narrow window to re-engage Iran in serious talks. Officials in Tehran must re-open their facilities to international inspectors and work to come back into compliance with their nuclear obligations. Iran has vowed retribution if sanctions snap back, and the renewed tension could cause further instability in a region just emerging from a month of war.

The snapback provision will soon expire. Under the 2015 Joint Comprehensive Plan of Action (JCPOA), member nations of the U.N. can “snap back” all UN sanctions against Iran if it is found to be in violation of the agreement. The provision itself expires in October, leaving Europe little time to act.

Iran’s nuclear program has far exceeded the limits set in the JCPOA since the Trump administration pulled out of the deal. Iran insists its program is still peaceful in nature, but recent data indicate its uranium stockpile and enrichment levels are on the cusp of reaching weapons-grade material.

“This is a very important development,” Rafael Grossi, head of the U.N. nuclear watchdog, the International Atomic Energy Agency (IAEA), told reporters Wednesday. “Going back to the original JCPOA would be almost impossible.”

U.S. Secretary of State Marco Rubio coordinated the snapback decision with his European counterparts this week, describing it as “a very powerful piece of leverage on the Iranian regime.”

Inspectors Welcome Back to Nuclear Facilities

Iran’s parliament passed legislation to end all cooperation with international inspectors at the start of August, but recent evidence suggests IAEA inspectors have returned to Iranian nuclear facilities. Grossi confirmed Wednesday that inspectors were on site at Bushehr nuclear power plant.

“We are there, today we are inspecting Bushehr,” he told reporters in Washington. “We are continuing the conversation so that we can go to all places, including the facilities that have been attacked.”

The IAEA’s safeguards are based on the Nuclear Non-Proliferation Treaty (NPT). Iran remains a signatory to that treaty and could face more domestic fallout if it were to also leave the NPT in response to snapback sanctions. Reports suggested that one of the choices Tehran had in such an event is leaving the NPT.

Iranian Foreign Minister Abbas Araghchi also confirmed Wednesday that inspectors were present at Bushehr to monitor fuel replacement, as the plant recently suffered a power failure. However, he rejected claims that the move was part of any broader agreement with IAEA for “new cooperation.”

Aftermath of the June War

Iran’s nuclear program was dealt a significant blow in June when Israel reportedly carried out a surprise strike on its nuclear facilities. Iran’s immediate response was a 12-day military campaign during which it and its proxies fired rockets at Israeli cities. In the final days of the conflict, U.S. forces also joined in, hitting three Iranian sites.

The IAEA had to withdraw its inspectors in July, as the war had made any effective monitoring impossible. Satellite images in the following weeks revealed that entrances to the Isfahan Nuclear Technology Research Center had been damaged in the fighting.

Tehran responded to the agency’s withdrawal by arguing that IAEA was giving Israel the justification it needed for its attack, by pointing out the lapses in Iranian compliance with its safeguard rules.

Iran Divided on the Issue at Home

Iran’s re-admittance of IAEA inspectors to some of its facilities has already prompted internal backlash. Parliamentary member Kamran Ghazanfari lambasted the remarks of speaker Mohammad Bagher Ghalibaf in support of allowing inspectors back into certain sites as an “explicit violation” of legislation suspending IAEA cooperation.

The legislation was passed after the war as part of an attempt to “counter the foreigners’ oppressive moves and psychological warfare waged against the Islamic Republic of Iran, especially with the belligerence of the IAEA” and related “discriminatory behavior by a few member states,” according to a statement posted on the parliamentary news site ICANA.

Negotiations by the European powers have been going on for some time as a diplomatic backchannel in case sanctions were to snap back on Iran. The European negotiators met with Iranian counterparts in Geneva on Tuesday as part of a last-minute effort to avoid triggering the mechanism. One European official close to the talks said there was little sign of progress.

Talks were also underway between U.S. envoy Steve Witkoff and Iran in Geneva prior to the June conflict. However, those talks were suspended when hostilities broke out.

Grossi would not say whether he thought Iran would remain open to talks in the coming month. “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.