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Germany, France and the United Kingdom will trigger the reimposition of U.N. sanctions on Iran as early as Thursday, three European officials told CNN Wednesday. The move sets in motion a 30-day “snapback” mechanism that was included in the 2015 Iran nuclear deal, officials said.

European leaders will use the coming month in a last-ditch diplomatic effort to convince Tehran to return to negotiations, open its facilities to international inspectors and begin taking steps to come back into compliance with its nuclear obligations.

Iran has said it will retaliate harshly if sanctions are reimposed, raising the risk of further violence in the Middle East, which has been roiled by conflict for the last month.

Snapback is a provision of the 2015 Joint Comprehensive Plan of Action (JCPOA) which allows members to reinstate U.N. sanctions on Iran if they find the country has violated the agreement.

The authority to reimpose those sanctions is set to expire in October, which is hastening the current efforts by European governments to negotiate some form of diplomatic settlement.

Iran’s nuclear program has advanced beyond JCPOA limits since former President Donald Trump withdrew from the agreement in 2018. Although Iran says its nuclear program is for peaceful purposes only, inspectors and analysts say the nuclear capabilities are quickly approaching weapons grade.

“Iran’s already decided to do other things in ways that are taking them much further than ever before,” U.S. Secretary of State Antony Blinken said Wednesday. “Going back to where the JCPOA was would be almost impossible,” Rafael Grossi, the head of the International Atomic Energy Agency (IAEA) added Wednesday.

Rubio, the U.S. secretary of state, who spoke with his European counterparts this week, described snapback as “a very powerful piece of leverage on the Iranian regime.”

Iran’s parliament passed a law in July that would cut off cooperation with international inspectors. But the IAEA has said teams were back on the ground in Iran earlier this month and were back in the country on Wednesday.

“The Agency’s inspectors were in Bushehr today,” Grossi told reporters in Washington. “Today we are inspecting Bushehr,” he added. “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 backed by the Nuclear Non-Proliferation Treaty (NPT). Iran is a signatory to the NPT and is required to allow inspections. However, one option the Iranian parliament is considering if sanctions are reinstated is to withdraw from the NPT, according to Reuters.

Iranian Foreign Minister Abbas Araghchi confirmed that IAEA inspectors were on the ground at the Bushehr nuclear power plant. Araghchi said they were there to monitor the plant as work was being done to replace fuel. He also said they were back because the Supreme National Security Council made the decision, which includes the foreign minister, but added that it did not signal any new form of “cooperation.”

Iranian Foreign Minister Abbas Araghchi makes a statement at the New Year reception of the Iranian Diplomatic community in Tehran, Iran, Thursday, Jan. 1, 2015. Iran, after having severed ties with the U.N. nuclear watchdog a week ago, has agreed to resume its cooperation with the agency to work on a deal that would ease economic sanctions imposed on the country, the agency’s chief said Thursday.

Tensions between Iran and Israel flared in June when the Jewish state launched a series of strikes on Iranian nuclear facilities. The 12-day conflict also saw Iranian attacks on Israeli cities, and in the final days U.S. forces were drawn into the conflict with Iran when they struck three Iranian sites.

The IAEA said it withdrew its inspectors in July, after conditions in the country during the conflict made it impossible to monitor what was happening at Iranian nuclear sites. Satellite images showed entrances to Iran’s Isfahan Nuclear Technology Research Center had been damaged, which Iran said was done by the Israelis during their June strikes.

Iran had long accused the agency of trying to provide a pretext to Israel’s strikes by publicizing information that Iran was not complying with safeguard rules.

The decision to allow the IAEA inspectors back into Iran has drawn some criticism from within the country. Parliamentary member Kamran Ghazanfari condemned recent comments by Speaker Mohammad Bagher Ghalibaf, that Iran should allow limited inspections at some facilities. Ghazanfari called the comments an “explicit violation” of the laws suspending cooperation with the IAEA.

The legislation was passed by the Iranian parliament after the June conflict and was said to be to counter foreign aggression and interference as well as perceived bias by IAEA inspectors.

European negotiators spoke with Iranian officials in Geneva on Tuesday in a last-minute effort to persuade Tehran to negotiate and prevent the snapback from being triggered. Sources told CNN on Tuesday that little headway was made in the talks.

The U.S. was also engaged in talks with Iran ahead of the conflict through envoy Steve Witkoff, as they tried to work on a new nuclear deal. Those discussions came to a halt when the fighting started.

Grossi said he was “hopeful we may have a de-escalation in the next 30 days.” “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 added.

For now, however, Iran is facing diplomatic pressure from the West and internally as well, as lawmakers in parliament push to leave the NPT and others remain angry at the inspection decision. With snapback set to expire in October, the next few weeks could prove pivotal as to whether diplomacy is possible or sanctions and confrontation become the norm.