Britain, France, and Germany have warned they are prepared to reimpose United Nations sanctions on Iran if it fails to return to nuclear negotiations before the end of August.

In a letter to the UN dated Friday last week, the three countries, collectively known as the E3, said they were ready to trigger the “snapback” mechanism, which allows a single Western party to reinstate sanctions if Tehran breaches its commitments.

French Foreign Minister Jean-Nöel Barrot shared the letter on social media on Wednesday, co-signed by his German and British counterparts.

“We have made clear that if Iran is not willing to reach a diplomatic solution before the end of August 2025, or does not seize the opportunity of an extension, E3 are prepared to trigger the snapback mechanism,” the letter stated, adding that their priority remained ensuring Iran does not develop a nuclear weapon.

The warning follows months of diplomatic deadlock, intensified by a 12-day war between Iran and Israel in June, during which Israeli and U.S. airstrikes targeted nuclear-related facilities in Iran. Last month, E3 officials met Iranian representatives in Istanbul to discuss the possible return of sanctions lifted under the 2015 nuclear deal, which restricted Iran’s nuclear activities in exchange for relief.

Tehran’s Foreign Ministry spokesman, Esmail Baghaei, had urged the European nations to reconsider what he described as their “previous unconstructive attitude.” But since the conflict, Iran has suspended cooperation with the International Atomic Energy Agency (IAEA), and the watchdog’s first post-war visit this week did not include inspections of nuclear sites.

German Foreign Ministry spokesperson Josef Hinterseher said Wednesday the legal basis for snapback sanctions “has long existed” but stressed that “Iran still has the choice” to resume diplomacy and full cooperation with the IAEA.

The IAEA and U.S. intelligence agencies maintain that Iran’s organized nuclear weapons program ended in 2003, though the country has been enriching uranium to 60%, just below weapons-grade levels of 90%.