The signatories to the Iran nuclear deal on Tuesday said they stood by the faltering accord, opposing US efforts to restore international sanctions on the Islamic republic.

Britain, France, Germany, China and Russia are struggling to save the landmark 2015 accord with Iran, which has been progressively stepping up its nuclear activities since the US pulled out of the deal in 2018.

Tehran insists it is entitled to do so under the terms of the accord – which swapped sanctions relief for Iran’s agreement to scale back its nuclear programme – following Washington’s withdrawal and re-imposition of sanctions.

EU senior official Helga Schmid, who chaired the talks in Vienna on Tuesday, wrote on Twitter that the meeting’s participants were “united in resolve to preserve the #IranDeal and find a way to ensure full implementation of the agreement despite current challenges”.

In a later statement, she added that all parties reiterated that “the US cannot initiate the process of reinstating UN sanctions” by drawing on a UN resolution enshrining the nuclear accord, which they have left.

Representatives from Britain, China, France, Germany, Iran and Russia all attended the talks – part of a regular series of gatherings to discuss the accord, which has been increasingly tense since the US pullout began unravelling the agreement.

China’s representative, senior Ministry of Foreign Affairs official Fu Cong, told reporters after the meeting that Iran needed to come back to full compliance, but at the same time “the economic benefit that is due to Iran needs to be provided”.

He slammed the US for “making a mockery of international law” in its “attempt to sabotage and to kill the JCPOA”, referring to the abbreviation of the deal’s formal name, the Joint Comprehensive Plan of Action.

Russian Deputy Minister of Foreign Affairs Sergei Ryabkov was also quoted by Russian news agency RIA Novosti as saying participants were united in their “general, unanimous lack of recognition” of Washington’s move.

The UN last week blocked the US bid to re-impose international sanctions on Iran.

Washington also failed to rally enough support to extend an arms embargo on Iran that is scheduled to start being rolled back from next month.

In a boost to Tuesday’s talks, the Iranian atomic energy agency last week also agreed to allow inspectors of the UN nuclear watchdog to visit two sites suspected of having hosted undeclared activity in the early 2000s.