Formally known as the Joint Comprehensive Plan of Action (JCPOA), the 2015 deal offered sanctions relief in exchange for curbs on Tehran's nuclear ambitions and guarantees it would not seek an atomic bomb.

But the accord has been hanging by a thread since former US president Donald Trump unilaterally withdrew from it in 2018 and reimposed punishing sanctions on Tehran.

"To resolve this urgent task, we believe it is perfectly possible to work out synchronous steps -- simultaneous steps to be taken in stages by both the Iranians and the United States," Russian Foreign Minister Sergei Lavrov said.

"If we deliberate on which side should be first to return to compliance, then this bargaining could go on forever," he told reporters during a visit to Abu Dhabi.

Following Joe Biden's US presidential election victory in November, Washington, Tehran and the European parties to the deal -- France, Germany and Britain -- have been trying to salvage it.

Biden has signalled his readiness to revive the accord, but insists Iran first return to all its nuclear commitments, most of which it suspended in response to the US sanctions.

Tehran meanwhile demands Washington take the first step by scrapping the sanctions.