France, Germany and Britain have warned they are prepared to reinstate United Nations sanctions on Iran if it does not return to negotiations over its nuclear programme, according to a letter sent to the U.N. on Tuesday.

The foreign ministers of the so-called E3 group raised the prospect of invoking the “snapback” mechanism unless Tehran engages before the end of August, according to a letter shared by the French foreign ministry, confirming details first reported by the Financial Times and Le Monde.

“We have made it 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 ministers wrote.

The letter added that the E3 had offered a limited extension to allow for direct negotiations between the United States and Iran, but said Tehran had so far left the proposal unanswered.

The three European powers, alongside China and Russia, remain parties to the 2015 nuclear agreement that lifted sanctions on Iran in exchange for curbs on its nuclear activity. The United States withdrew from the accord in 2018.

The letter described last month’s meeting in Istanbul with Iranian officials as “serious, frank and detailed”, the first face-to-face talks since Israeli and U.S. strikes on Iran’s nuclear sites in June.

Iranian lawmaker Manouchehr Mottaki, who served as foreign minister from 2005 to 2010, said parliament “has its finger on the trigger” to withdraw from the nuclear Non-Proliferation Treaty (NPT) if sanctions are reimposed through the snapback process.

Speaking to Iran’s semi-official Defa Press, Mottaki said lawmakers would approve a bill to leave the 2015 deal within 24 hours of such a move.

Tehran previously signalled during its 12-day conflict with Israel in June that it was preparing legislation to exit the NPT, which Iran ratified in 1970. The treaty allows states to pursue civilian nuclear energy while renouncing nuclear weapons and cooperating with the U.N. International Atomic Energy Agency (IAEA).

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