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Germany, France and the United Kingdom are on the verge of invoking a return of United Nations sanctions on Iran, three European officials told CNN on Wednesday. The so-called “snapback” mechanism, part of the 2015 Iran nuclear deal, could be initiated as soon as Thursday.

The procedure takes 30 days to take full effect, giving time for diplomacy to work. European leaders are hoping Tehran will use that time to come to the negotiating table, open its facilities to inspectors and take other steps toward complying with nuclear obligations.

Iran has threatened to retaliate harshly if sanctions are reimposed, raising the possibility of further turmoil in a region still reeling from last month’s conflict.

Snapback deadline nears

The snapback provision in the 2015 Joint Comprehensive Plan of Action (JCPOA) allows members to reinstate UN sanctions in the event of a violation by Iran. The authority to do so under the JCPOA will expire in October.

Iran has since increased its nuclear program far beyond JCPOA limits, after former President Donald Trump withdrew the United States from the deal. Tehran maintains that its nuclear work is for peaceful purposes only. But inspectors and analysts say that Iran is nearing capabilities that could be used to develop nuclear weapons.

“It’s 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 with European counterparts on Iran this week, called the snapback “a very powerful piece of leverage on the Iranian regime.”

Inspectors return as tensions rise

Inspectors returned to Iran after the country’s parliament had passed a law ordering a cessation of cooperation with the IAEA, Grossi announced Wednesday. He said on Twitter that the team is “on the ground” and that inspectors were at the Bushehr nuclear power plant on Wednesday.

“The Bushehr power plant is operating normally and the IAEA inspectors are monitoring the replacement of the nuclear fuel at the reactor,” Iranian Foreign Minister Abbas Araghchi said Wednesday.

“Today we are inspecting Bushehr,” Grossi said to 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 authority for safeguards monitoring derives from the Nuclear Non-Proliferation Treaty (NPT), to which Iran is still a signatory. Tehran is reportedly considering withdrawing from the NPT in the event of sanctions snapback.

Iran’s foreign minister said that the Bushehr presence is limited to monitoring the replacement of the reactor’s nuclear fuel following a decision by the Supreme National Security Council. He denied that the move represents a new deal for “new cooperation.”

Recent conflict between Iran and Israel

A strike by Israel on Iran’s nuclear facilities in June touched off a 12-day conflict. Tehran retaliated with missile strikes on Israeli cities. U.S. forces entered the conflict in the final days, hitting three Iranian sites.

The IAEA withdrew its inspectors in July, saying they were unable to monitor nuclear sites during wartime. Satellite images published later showed signs of damage to the entrances of Iran’s Isfahan Nuclear Technology Research Center.

Iran accused the IAEA of giving Israel “green light” to attack, by publicizing the country’s non-compliance with safeguarding rules.

Iran division over the decision

The decision to allow IAEA inspectors into some facilities has been met with some resistance in Iran. Parliamentary member Kamran Ghazanfari lambasted parliamentary Speaker Mohammad Bagher Ghalibaf for comments on Tuesday that appeared to back a limited resumption of IAEA inspections.

Ghalibaf’s statements “are an explicit violation of the [parliamentary decision] to suspend cooperation with the IAEA,” Ghazanfari wrote on Twitter.

The June legislation came after the conflict, which Iran has framed as part of an effort to push back against foreign aggression and perceived partiality in IAEA reports.

Diplomacy likely lost

European negotiators met with Iranian officials on Tuesday in Geneva in a last effort to avoid sanctions snapback. But they signaled there was little progress.

U.S. envoy Steve Witkoff was also engaged in diplomatic outreach to Tehran ahead of the Israel-Iran conflict, with the aim of hashing out a new nuclear deal. Those talks were derailed when the fighting broke out in June.

Grossi is holding out hope that Iran could de-escalate over the next month. “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 Wednesday.

For now, though, Iran finds itself facing pressure from the West as well as from within. With the snapback deadline approaching, the next several weeks will likely determine whether diplomacy survives or whether sanctions and confrontation mark the next phase of Iran’s nuclear ambitions.