Germany, France and the United Kingdom are expected to trigger the reimposition of United Nations sanctions on Iran, three European officials told CNN on Wednesday. The so-called “snapback” mechanism could be set in motion as soon as Thursday as part of the 2015 Iran nuclear deal.

The process takes 30 days to complete, leaving a narrow window for diplomacy. European leaders are hopeful that Tehran will use the time to reengage in serious talks, open its facilities to international inspectors, and take corrective measures to fall in line with its nuclear obligations.

But Iran has threatened severe retaliation if sanctions return, and there is the potential of more tumult in a region that has already seen significant conflict in recent weeks.

The snapback provision in the 2015 Joint Comprehensive Plan of Action (JCPOA) allows members of the deal to restore UN sanctions if Iran violates the agreement. The authority to use the snapback expires in October, so the European Union has a sense of urgency about the matter.

Iran has since ramped up its nuclear program far beyond the limits of the JCPOA after the United States withdrew from the agreement under former President Donald Trump. Tehran maintains the program is peaceful, but inspectors and analysts say it is drawing ever closer to weapons-grade capabilities.

“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 met with his European counterparts to coordinate this week, called the snapback mechanism “a very powerful piece of leverage on the Iranian regime.”

Inspectors have been back in recent days despite legislation passed by Iran’s parliament that ordered them to cease cooperation with international inspectors. IAEA teams were at the Bushehr nuclear power plant on Wednesday, Grossi confirmed.

“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 derive from the Nuclear Non-Proliferation Treaty (NPT), and Iran is still a signatory to that. According to The Times of Israel, one of the options Tehran is considering if sanctions snap back is withdrawal from the NPT.

Iranian Foreign Minister Abbas Araghchi said the inspectors were there to make sure fuel replacement work at Bushehr proceeded smoothly. He said the decision to allow them to do so was made by Iran’s Supreme National Security Council, which would not have approved if there were no agreement. Araghchi denied there was any new understanding with the IAEA for “new cooperation.”

Fallout from the recent conflict

Iran’s nuclear facilities were hit in a series of strikes by Israel in June, which set off a 12-day conflict in the region. Iranian forces targeted Israeli cities with ballistic missiles in retaliation, and U.S. forces joined in the final days to hit three Iranian sites.

The IAEA withdrew its inspectors in July after the onset of the conflict. It said in a statement at the time that the invasion by Israel had “created an impossible environment for the IAEA to continue with the presence and effective implementation of the necessary safeguards in Iran.”

Satellite images later showed damage to two entrances at the Isfahan Nuclear Technology Research Center. Iran said it was at Bushehr that the Israelis attacked.

Tehran later accused the IAEA of giving Israel the pretext to launch its strikes by publicizing that Iran had failed to meet a number of safeguard rules.

Divisions inside Iran

Allowing IAEA inspectors to reenter the Bushehr nuclear power plant has drawn criticism in Iran’s own parliament. Parliamentary member Kamran Ghazanfari criticized Speaker Mohammad Bagher Ghalibaf’s recent comments that his nation was open to a limited continuation of the IAEA inspections.

Ghazanfari wrote that the remarks by Ghalibaf, who is also head of the Islamic Revolutionary Guard Corps, “amount to an explicit violation of the law on suspending cooperation with the agency and receiving its officials and are an insult to the honorable representatives of the people.”

Iran’s parliament had passed the legislation ordering a halt to cooperation with the agency in the wake of the June conflict. At the time, lawmakers said the move was in self-defense against foreign aggression and the IAEA’s “biased and discriminating approach against Iran.”

Diplomatic window narrows

European negotiators met with Iranian representatives in Geneva on Tuesday in a last-minute effort to head off the sanctions. But the sources indicated that little progress was made.

Ahead of the conflict, U.S. envoy Steve Witkoff had been involved in diplomatic talks to negotiate a new nuclear agreement, but those collapsed with the outbreak of fighting.

Grossi was more optimistic that the next month could be used to de-escalate the situation. “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, Iran is feeling increasing pressure from outside forces and its own political system. With the snapback mechanism about to expire in October, the next several weeks will determine if diplomacy can continue — or if sanctions and confrontation will characterize the next chapter in Iran’s nuclear history.