Germany, France, and the United Kingdom are expected to trigger the reimposition of United Nations sanctions on Iran as soon as this week, according to three European officials who spoke with CNN on Wednesday. Known as the “snapback” mechanism, the process may be activated as soon as Thursday. It takes a month for the sanctions to be fully reinstated, leaving a narrow window for diplomacy before they take effect.

European officials hope that Iran will use that time to reengage in meaningful negotiations, open its doors to international inspectors, and take concrete steps toward fulfilling its nuclear obligations under the 2015 deal.

But Iran has threatened a “harsh” response if sanctions are reimposed and this week’s military action has increased the likelihood of further regional instability.

Triggering the Snapback Mechanism

European efforts to force Iran to return to the table are partly driven by a looming deadline. The authority to trigger the snapback provision of the 2015 Joint Comprehensive Plan of Action (JCPOA), which could restore United Nations sanctions on Tehran, will expire in October.

Iran has since accelerated its nuclear program beyond the limits of the JCPOA in response to the Trump administration’s withdrawal from the deal.

Inspectors and analysts say Tehran’s capabilities are growing closer to the threshold of producing a nuclear weapon, while Iranian officials continue to insist that their program is peaceful.

“It is 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 this week with European counterparts to coordinate on the issue, called the snapback mechanism “a very powerful piece of leverage on the Iranian regime” in a statement on Tuesday.

Inspectors Return, Monitoring Continues

Iran’s parliament has passed legislation that would end cooperation with international inspectors, but IAEA teams have returned to the country in recent weeks.

Grossi confirmed Wednesday that inspectors were on site at the Bushehr nuclear power plant in southern Iran, where they were scheduled to monitor the replacement of fuel inside a reactor.

“Today we are inspecting Bushehr. This is on going. We are continuing the conversation so that we can go to all places, including the facilities that have been attacked,” Grossi told reporters in Washington.

IAEA safeguards are based in the Nuclear Non-Proliferation Treaty (NPT), which Iran has not abandoned. The country is reportedly considering withdrawal from the NPT if sanctions are reinstated.

Iranian foreign ministry spokesman Abbas Araghchi said the IAEA inspectors were permitted to monitor the Bushehr reactor’s fuel replacement as a result of a decision by the Supreme National Security Council. He denied the IAEA’s reports that the move was part of “new cooperation.”

Bombings, Accusations of Bias Follow Conflict

Tensions between Iran and the West have sharply deteriorated since June, when Israel bombed Iran’s nuclear facilities, sparking a 12-day conflict.

Iran retaliated with rocket attacks on Israeli cities, and in the final days the United States and its forces joined the fray with strikes on three Iranian sites.

The IAEA had withdrawn its inspectors in July, citing the impossibility of monitoring in wartime. Months later, satellite images revealed Iranian military had blown up the entrance to the Isfahan Nuclear Technology Research Center.

Tehran has since accused the IAEA of aiding the Israeli attack by publicizing instances of Iranian non-compliance with safeguard regulations.

Political Fallout from War Raises Barriers

The IAEA has also come under fire in Iran for returning inspectors to at least some of the country’s nuclear facilities. Iranian foreign ministry spokesman Araghchi said on Wednesday that the return of the inspectors to Bushehr was “specific and limited,” while denying that the Council had approved “new cooperation.”

The decision to end cooperation with IAEA inspectors was made by Iran’s parliament following the June conflict.

It was framed as a measure to prevent foreign intelligence gathering and to avoid biased reporting of Iran’s nuclear activity by the IAEA.

This week’s move to return some inspectors has met with criticism at home. Parliamentary member Kamran Ghazanfari on Wednesday condemned the comments of Iranian parliament speaker Mohammad Bagher Ghalibaf in support of limited inspections, saying they were an “explicit violation” of the law suspending cooperation with the agency.

European Diplomacy Has Had Little Success

European negotiators met with Iranian representatives in Geneva on Tuesday in a last-ditch effort to avert the sanctions.

But according to sources, there was little indication of movement on either side. Earlier in the month, before the outbreak of conflict between Iran and Israel, U.S. envoy Steve Witkoff had been engaged in his own diplomatic push to forge a new nuclear agreement with Iran.

That dialogue, too, has now ended.

Grossi hopes the next month may bring 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 with domestic and international pressure mounting on Tehran, it remains to be seen whether Iran will agree to reengage in diplomacy. With the snapback mechanism set to expire in October, the next month may decide whether diplomacy is given a chance to survive in the face of confrontation.