The Biden administration has hailed a potential breakthrough in deadlocked efforts to revive the Iranian nuclear deal after Tehran agreed to talks through European allies.
Britain, the EU, China, Russia, France and Germany will meet separately with the US and Iran for negotiations in Vienna this week - marking the first major progress in attempts to return both countries to the 2015 accord.
US president Joe Biden has promised to rejoin the agreement on condition Iran first returns to respecting commitments it abandoned after Donald Trump pulled out of the deal and reimposed sanctions.
Tehran, however, has said Washington must end the sanctions before it will make any moves to get back in line.