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Germany, France, and the United Kingdom will soon invoke a process to reimpose United Nations sanctions on Iran, three European officials told CNN on Wednesday. The so-called “snapback” mechanism, included in the Iran nuclear deal of 2015, can be activated as early as Thursday.

The process would take 30 days to go into effect, leaving a window for diplomacy. European leaders hope Iran will use the time to reengage in meaningful negotiations, allow access to its facilities for international inspectors, and reverse its current course away from nuclear obligations.

Iran, for its part, has threatened severe retaliation if sanctions are reimposed, which many fear could lead to further unrest in a Middle East already rattled by recent fighting.

Snapback Mechanism Expiring Soon

Snapback is part of the 2015 Joint Comprehensive Plan of Action, or JCPOA. It allows members to reinstate United Nations sanctions on Iran if it fails to abide by the deal. The ability to use that mechanism will expire in October.

Iran has since accelerated its nuclear program well past the limits of the JCPOA after former President Donald Trump pulled the United States out of the agreement. Tehran insists it has not been trying to build a nuclear weapon and that its program is peaceful. But inspectors and analysts have noted it is rapidly reaching the point of no return to weapons-grade levels of enrichment.

“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 to his European counterparts on the matter earlier this week, said that using snapback was “a very powerful piece of leverage on the Iranian regime.”

Inspectors Return to the Field

Inspectors from the IAEA have returned to Iran in recent days despite legislation passed by the Iranian parliament calling for a halt to cooperation with international inspectors.

Grossi confirmed on Wednesday that IAEA teams were at the Bushehr nuclear power plant in Iran, where workers were replacing fuel rods after the facility lost cooling water in a suspected Israeli attack.

“Today we are inspecting Bushehr,” Grossi 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 has insisted it is operating under its “non-negotiable” safeguards, which stem from the Nuclear Non-Proliferation Treaty, or NPT, of which Iran is still a signatory. But according to the Financial Times, one of the options Tehran is considering if the sanctions snapback goes through is withdrawing from the NPT.

Iranian Foreign Minister Abbas Araghchi said the inspectors had come to Bushehr to monitor the fuel replacement, which they were allowed to do under a Supreme National Security Council decision. But he denied the move indicated any agreement for “new cooperation.”

Conflict Escalation

The conflict began after Israel hit Iranian nuclear facilities in June. Iran retaliated by striking Israeli cities for 12 days in a row. U.S. forces eventually entered the fight in the last three days, bombing three Iranian sites.

The IAEA inspectors left Iran in July, saying the conditions on the ground during the fighting made their presence untenable. Months later, satellite images showed entrances to Iran’s Isfahan Nuclear Technology Research Center that had been damaged.

Iran charged that the IAEA had been “setting the stage” for Israel to attack by publicizing Tehran’s non-compliance with IAEA safeguard regulations.

Parliamentary Pushback

The decision to allow IAEA inspectors into Bushehr and other nuclear facilities has not been well received by Iran’s parliament. Kamran Ghazanfari, a parliamentary member, criticized speaker Mohammad Bagher Ghalibaf for allowing limited inspections, saying it was an “explicit violation” of the law suspending the inspections.

Iran’s parliament had passed the legislation to suspend cooperation with the IAEA after the June conflict. It said in the legislation that such actions were necessary to “prevent crimes and aggression by arrogant powers” and to “confront foreigners’ biased approach” to reports on Iran’s nuclear program.

Last Chance for Diplomacy

European diplomats held a meeting with Iranian counterparts in Geneva on Tuesday in a last-ditch effort to avoid sanctions. But the sources with knowledge of the meeting said there was little progress toward any kind of agreement.

The United States, through envoy Steve Witkoff, had been in talks with Iran earlier this year to develop a new nuclear agreement but that process ground to a halt when fighting began in June.

Grossi said he was cautiously optimistic that over the course of the next month there would be an opportunity to de-escalate. “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, though, Iran is facing increasing pressure from both European allies and its own parliament. With the snapback process set to expire in October, the next month will likely determine whether or not diplomacy can survive or whether sanctions and retaliation will chart the course for the next stage of Iran’s nuclear development.