Germany, France and the United Kingdom will soon trigger the reimposition of United Nations sanctions against Iran, three European officials said Wednesday. The “snapback” mechanism, part of the 2015 nuclear deal with Iran, may be activated as soon as Thursday.

It takes 30 days for sanctions to be reimposed through the process, leaving a narrow window of opportunity for diplomacy. European leaders are hoping Tehran will use that time to recommit to meaningful negotiations, open up its nuclear facilities to international inspectors and take steps to return to compliance with its nuclear commitments.

But Iran has also threatened “extreme reactions” if sanctions are re-imposed. The return of sanctions would ratchet up pressure on Tehran, which faces economic distress and discontent at home. Some fear that snapback could cause new unrest in a region already roiled by conflict in recent weeks.

Deadline Looms for Snapback

Under the 2015 Joint Comprehensive Plan of Action, a UN mechanism allows for the restoration of all previous sanctions if the other parties to the deal determine Iran is in violation of the agreement. That right will expire in October.

Iran has since accelerated its nuclear program to levels beyond the JCPOA limits following former President Donald Trump’s withdrawal from the deal. Tehran maintains its program is peaceful, but inspectors and outside analysts have said Iran is approaching weapons-grade levels.

“Iran’s nuclear program is advancing very quickly,” Rafael Grossi, head of the International Atomic Energy Agency, said on Wednesday. “Going back to the original JCPOA would be almost impossible.”

U.S. Secretary of State Marco Rubio coordinated with his European counterparts on snapback this week, the State Department said. “I do believe this is a very powerful piece of leverage on the Iranian regime,” Rubio said Wednesday.

IAEA Inspectors Return

Iran’s parliament in July passed a law that would stop cooperation with international inspectors, but IAEA teams have recently been back on the ground. Grossi said on Wednesday that inspectors were in place at the Bushehr nuclear power plant.

“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 stem from the Nuclear Non-Proliferation Treaty (NPT), of which Iran is a signatory. The JCPOA built off those commitments, but Tehran reportedly has considered withdrawal from the NPT if sanctions are reimposed.

Iranian Foreign Minister Abbas Araghchi said the inspectors were at Bushehr to monitor the replacement of fuel after a decision by Iran’s Supreme National Security Council. Araghchi told reporters that does not indicate a “new cooperation” between Tehran and the IAEA.

The tensions over Iran’s nuclear program and possible snapback of sanctions are coming on the heels of recent conflict in the region.

In June, Israel struck Iran’s nuclear facilities, setting off a 12-day war. Iranian forces and allies then launched attacks on Israeli cities. In the conflict’s final days, U.S. forces also joined the fray, striking three Iranian sites.

The IAEA said in July it was withdrawing its inspectors from Iran, saying the conditions in the war made it too difficult to monitor. Satellite imagery later showed doors and access points damaged at Iran’s Isfahan Nuclear Technology Research Center.

The IAEA, under Grossi, also became a target of Iranian ire for publishing the information that Israel ultimately used to justify its strike on the nuclear facilities, Tehran said.

Iran Divided at Home

The decision to let the IAEA inspectors return to the Bushehr nuclear facility and a natural gas facility in the holy city of Qom is controversial inside Iran. Parliamentary member Kamran Ghazanfari attacked Speaker Mohammad Bagher Ghalibaf for making comments that seemed to back limited inspections, which Ghazanfari said was “an explicit violation” of the laws passed to suspend cooperation with the IAEA.

Iran’s parliament approved the legislation following the June conflict, saying it was aimed at defending Iran against foreign attacks and an “obsessed, and unfair” IAEA.

Negotiations Continue

European negotiators met with Iranian counterparts in Geneva on Tuesday in what one source described as “an effort to understand” if Tehran would be willing to stop the snapback process. European officials had earlier been trying to reach Tehran but had little success.

In the weeks before the June conflict, U.S. envoy Steve Witkoff was engaged in diplomatic negotiations with Iran in a bid to lay the groundwork for a new nuclear deal. Those talks were cut short by the outbreak of conflict.

Grossi struck a cautiously optimistic tone on Wednesday. “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.