Talks to revive a 2015 nuclear deal between Western powers and Iran are approaching a dangerous impasse, British Foreign Secretary Liz Truss said on Tuesday.

"This negotiation is urgent and progress has not been fast enough. We continue to work in close partnership with our allies but the negotiations are reaching a dangerous impasse," Truss told parliament.

"Iran must now choose whether it wants to conclude a deal or be responsible for the collapse of the JCPOA (nuclear deal). And if the JCPOA collapses, all options are on the table."