Britain, France and Germany on Saturday strongly condemned a US decision to end sanctions waivers for companies from nations that remain in a nuclear accord with Iran.
The waivers were part of the landmark agreement signed with Tehran in 2015 which sought to limit Iran's nuclear ambitions in return for lifting crippling economic sanctions.
They allowed European, Chinese and Russian companies to work on the conversion of a heavy water reactor in Arak, a major industrial city in western Iran.
"We deeply regret the US decision to end the three waivers covering key JCPOA [Joint Comprehensive Plan of Action] nuclear projects in Iran," read a joint statement from the three European powers.
"These projects, endorsed by UN Security Council Resolution 2231, serve the non-proliferation interests of all and provide the international community with assurances of the exclusively peaceful and safe nature of Iranian nuclear activities."
US Secretary of State Mike Pompeo announced the decision to end the waivers earlier this week.
The nuclear deal was signed by the US, Britain, China, France, Germany and Russia as well as Iran.
However, the US pulled out in 2018 and the latest decision on waivers, following further sanctions, raises the prospect that the agreement could collapse.
Russia has also attacked the decision by Mr Pompeo, with Moscow claiming US foreign policy was becoming "more dangerous and unpredictable".