U.S. envoy Robert Malley joined counterparts from France, Britain and Germany at the meetings in Paris, at what the French Foreign Ministry called a "critical time" in efforts to salvage the accord.
"It is urgent and crucial for Iran to end the activities of unprecedented gravity that it is conducting in violation of the (agreement) and to immediately resume full-fledged cooperation'' with the International Atomic Energy Agency, Foreign Ministry spokesperson Anne-Claire Legendre said in an online briefing.
The IAEA is charged with monitoring the 2015 accord, which was aimed at curbing Iran's nuclear activity in exchange for the lifting of crippling sanctions. The U.S. pulled out of the accord under Donald Trump and re-imposed sanctions.
Since then Iran has stepped up nuclear activity and is now in violation of several aspects of the deal, known as the Joint Comprehensive Plan of Action or JCPOA.
Iran's nuclear activity includes enriching uranium which Western nations fear could be used to build an atomic bomb. Tehran denies any such ambitions. The U.S. and European partners are ready to return immediately to negotiations with Iran "in order to swiftly conclude an agreement on Iran's return to its commitments and the United States' return to the JCPOA,'' Legendre said.
Iran's new hardline government led by President Ebrahim Raisi, which took power in August, has hinted it will return to the nuclear talks in Vienna but has balked at setting a date.