Germany, France, and the United Kingdom are on the verge of activating a mechanism that would reimpose United Nations sanctions on Iran, three European officials told CNN Wednesday. The so-called “snapback” process could be initiated as soon as Thursday.

The 30-day process that will see the sanctions reinstated has left little time for diplomacy. The hope among European leaders is that Tehran will use the coming month to come back to the table for serious negotiations, allow international inspectors back into its facilities, and take steps toward compliance with its nuclear obligations.

But Iranian leaders have threatened a harsh response if sanctions are reimposed, increasing the possibility of further instability in a region already roiled by the recent conflict.

The snapback mechanism is part of the 2015 Iran nuclear deal, the Joint Comprehensive Plan of Action (JCPOA). The provision in the agreement allows for the return of UN sanctions on Iran if it is found to be in violation of the accord. But the authority to snap back those sanctions is set to expire in October, making the current European push more urgent.

Iran has been expanding its nuclear program beyond the limits of the JCPOA since former U.S. President Donald Trump withdrew the United States from the deal. Iran has long maintained the program is peaceful in nature, but nuclear inspectors and outside experts say the country’s program is close to weapons-grade levels.

“Going back to the original JCPOA would be almost impossible,” International Atomic Energy Agency (IAEA) head Rafael Grossi said Wednesday.

U.S. Secretary of State Marco Rubio met with his European counterparts on Tuesday and Wednesday and told reporters that the snapback “is a very powerful piece of leverage on the Iranian regime.”

Inspectors Return, But Tensions Are High

In July, Iran’s parliament passed legislation to end cooperation with international inspectors. IAEA inspectors teams, however, have recently returned to the country. Grossi told reporters on Wednesday that inspectors were back at the Bushehr nuclear power plant.

“Today we are inspecting Bushehr,” he said during a meeting with reporters in Washington. “We are continuing the conversation so that we can go to all places, including the facilities that have been attacked.”

IAEA inspectors have safeguards rights under the Nuclear Non-Proliferation Treaty (NPT). Iran has not announced plans to withdraw from the treaty, but sources told Reuters that it was one option being discussed if sanctions are reimposed.

Iranian Foreign Minister Abbas Araghchi said in a statement Wednesday that inspectors were back at Bushehr to monitor fuel replacement there. The action came after a decision by Iran’s Supreme National Security Council, he said.

Iranian officials have said the move does not indicate a broader decision to start “new cooperation” with the IAEA. Araghchi called for “practical steps for a constructive cooperation with the IAEA.”

Fallout Continues Over Aftermath of Recent War

Iran’s nuclear facilities were the target of Israeli strikes in June that sparked a 12-day war. Iran’s retaliatory missile strikes during the conflict targeted Israeli cities and towns, and U.S. forces got involved toward the end of the conflict, striking three Iranian sites.

The IAEA in July withdrew its inspectors from Iran, saying it was no longer possible to conduct inspections during wartime. Satellite imagery taken after the conflict showed entrances to Iran’s Isfahan Nuclear Technology Research Center had been damaged.

Iran had accused the IAEA of “providing Israel with the excuse to strike” by reporting Iranian violations of safeguard rules.

Iran Divided on Decision to Allow IAEA Back In

The decision to let IAEA inspectors into at least some facilities has been met with criticism in Iran. Parliamentary member Kamran Ghazanfari said Speaker Mohammad Bagher Ghalibaf’s comments that certain facilities could be opened to inspectors was “an explicit violation” of the parliament’s laws suspending cooperation with the agency.

Iran’s parliament had approved the legislation suspending inspections after the June conflict. It described the law as necessary to defend against foreign attacks and what it saw as IAEA biased reporting on Iranian non-compliance.

European Diplomatic Efforts Continue, But Window Is Small

European negotiators met with Iranian representatives in Geneva Tuesday in what one source described as a last-minute effort to avert the sanctions. The source said little progress had been made in the meeting.

Before the conflict broke out, U.S. envoy Steve Witkoff was also involved in diplomatic efforts to reach a new nuclear deal. Those talks have ended as fighting has continued.

Grossi on Wednesday said that there was a chance that the next month could see a 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.

But for now, Iran finds itself under pressure both from Western nations and from elements within its own system. The snapback authority is set to expire in October, making the coming weeks pivotal for the future of diplomacy or if confrontation and sanctions will come to define the next chapter of Iran’s nuclear program.