Germany, France and the United Kingdom are expected to announce on Wednesday that they will trigger the reimposition of UN sanctions on Iran, three European officials told CNN.

The so-called “snapback” mechanism, which is enshrined in the 2015 Iran nuclear deal, could be activated as soon as Thursday.

European leaders are making a last-minute push for diplomacy before the process kicks in, a 30-day window during which Iran could reengage in negotiations and open its facilities to inspectors in order to comply with its nuclear obligations.

Iranian officials have promised a strong response to the sanctions’ return, which would escalate tensions in a region already destabilized by the fighting.

Under the 2015 Joint Comprehensive Plan of Action, or JCPOA, the snapback mechanism gives members of the United Nations the ability to return all sanctions against Iran if Tehran is in violation of the accord. The authority to use that mechanism expires in October.

Iran has been openly expanding its nuclear program well past JCPOA limits after the United States unilaterally left the agreement in 2018 under former President Donald Trump. Iran says its program is for peaceful energy purposes, but inspectors say its enrichment program is dangerously near levels that could be used to produce a nuclear weapon.

“What is crystal clear is that going back to the original JCPOA would be almost impossible,” Rafael Grossi, director general of the International Atomic Energy Agency, said Wednesday.

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

Inspectors Are Back

Inspectors from the IAEA returned to Iran this month, even as the country’s parliament passed legislation requiring the government to end cooperation with international inspectors.

The IAEA team was at Iran’s Bushehr nuclear power plant on Wednesday, Grossi said.

“In a few hours, we are inspecting Bushehr. We are at Bushehr. Today we are inspecting Bushehr,” Grossi said to 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 authority is based in the Nuclear Non-Proliferation Treaty, to which Iran is still a signatory. The country is considering withdrawing from the NPT if sanctions are reimposed, according to reports.

Iranian Foreign Minister Abbas Araghchi told the Associated Press that the inspectors were at Bushehr in order to monitor the fuel replacement there. A decision by the Supreme National Security Council allowed for that limited cooperation, but Araghchi denied that it signaled a “new cooperation.”

The Conflict

Tensions between Iran and Israel have surged in the last month following an Israeli strike on Iranian nuclear facilities in June that began a 12-day conflict.

Iran retaliated with a missile attack on Israeli cities. In the final days of the fighting, U.S. forces also struck three Iranian sites.

Inspectors pulled out of Iran in July, citing wartime conditions that would have put their safety at risk and prevent them from monitoring. Satellite imagery later revealed damage to doors at Iran’s Isfahan Nuclear Technology Research Center.

Iran said the IAEA gave Israel a pretext to attack its facilities by publicizing the fact that Tehran was in violation of safeguard rules in IAEA board meetings.

Divisions over IAEA Access

Allowing inspectors back into Iran’s facilities has sparked internal criticism from the Iranian government. Parliamentary member Kamran Ghazanfari accused the parliament’s Speaker Mohammad Bagher Ghalibaf of committing an “explicit violation” after Ghalibaf said last week that inspections of peaceful nuclear facilities could be allowed to continue.

Iran’s parliament passed legislation suspending all cooperation with the IAEA in July after the attack, saying that Israel had targeted the country’s civilian nuclear program in order to cover up its own nuclear ambitions. The IAEA’s reporting had falsely equated Tehran’s counter-strike to Israel as equally provocative, the legislation said.

Talks take place, but end with little progress

European negotiators met with Iranian counterparts on Tuesday in Geneva for last-minute talks over a renewed nuclear deal. Sources familiar with the meeting said little progress was made and European officials were preparing to announce the snapback.

Talks between U.S. envoy Steve Witkoff and Iran on a new nuclear agreement were also taking place ahead of the fighting, but came to an end when the attacks began in June.

Grossi expressed cautious hope on Wednesday that the next 30 days could offer an opportunity for de-escalation. “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.

The West now appears united on the snapback. The move was expected, but its timing was a subject of debate within the European Union last week after the U.S. announced its intentions to reinstate the snapback. European leaders were concerned that a joint announcement would allow the U.S. to control the narrative of the move and that separate announcements could create a confusing timeline that would limit diplomatic options.

The path for now is pressure, both from within the government and the Iranian political system, and from Western powers. The next month could determine if diplomacy lives or dies and if sanctions and confrontation will define the next chapter in Iran’s nuclear development.