Rob Malley, the US envoy on Iran, spoke with his counterparts from Britain, France and Germany on how diplomacy "continues to provide the most effective pathway" on Iran, State Department spokesman Ned Price said.

"We are united in the belief that negotiations should resume in Vienna as soon as possible and that they should resume precisely where they left off after the sixth round," Price told reporters in Washington.

The 2015 agreement between Iran and world powers to find a long-term solution to the now two-decade-old crisis over its controversial nuclear programme has been moribund since former US president Donald Trump walked out of the deal in May 2018.

His successor Joe Biden has said he is ready to re-enter the agreement, so long as Iran meets key preconditions including full compliance with the deal whose terms it has repeatedly violated by ramping up nuclear activities since Trump walked out.

But the Vienna-based talks through intermediaries made little headway, before being interrupted by the election of hardliner Ebrahim Raisi as Iran's president and suspended for the last four months.

Malley's trip to Paris comes after he visited the Gulf for talks with allies Qatar, Saudi Arabia and the United Arab Emirates which are all deeply concerned by Iran's nuclear programme.

The French foreign ministry said in a statement that the talks were coming at a "critical time" when France and other world powers were still prepared to return to the Vienna talks on bringing the US back into the deal.

"In the meantime, it is urgent and essential that Iran ends violations of unprecedented gravity" of the nuclear accord, the ministry said, urging Iran to also resume full cooperation with the UN atomic agency "without delay".

Western powers, Israel and pro-Washington Arabian peninsula states fear that Iran intends to develop an atomic bomb. Tehran denies this, insisting it only seeks to produce energy for its population.

UN nuclear watchdog chief Rafael Grossi expressed concern Tuesday that he was still waiting for a "high-level" discussion with Iranian officials, after negotiating last month a new compromise on monitoring Iran's nuclear programme to help restart the talks in Vienna.

Malley also met in Paris with Vice Foreign Minister Choi Jong-kun of South Korea, which is locked in a dispute with Iran over billions of dollars frozen to comply with US sanctions.

Price said that Malley and Choi discussed the "enforcement of the sanctions regime that continues to be in place and will continue to be in place on Iran unless and until there is a negotiated return to compliance."