US Secretary of State John Kerry met his Omani counterpart Youssef ben Alaoui in London on Wednesday, who is acting as an intermediary in crunch nuclear talks with Iran.
Kerry prolonged his stay in the British capital, where he has been since Monday, and will head to Paris Thursday before flying onto Vienna, where Tehran and six world powers are locked in a final round of negotiations.
Members of the "5+1" group (the United States, Russia, China, France, Britain and Germany) have until Monday to seal a landmark accord with Iran on its nuclear programme.
After their first meeting Tuesday, Kerry and Alaoui met briefly "to continue the discussion they had yesterday about the Foreign Minister`s trip to Tehran", a US State Department official said.
The top Omani diplomat, whose country has good relations with both Iran and the United States, had visited Tehran briefly on Sunday.
Oman has been acting as an intermediary in negotiations between Washington and Tehran on the Iranian nuclear programme, particularly since the last round of talks in Muscat in early November and in discussions held in secret in 2011-2012.
Diplomatic relations between the two countries have remained severed since April 1980, just after the Islamic Revolution.
As well as negotiating on the nuclear issue as part of the "5+1" group, the United States has been involved in bilateral discussions with Iran, under the aegis of the European Union`s foreign policy chief Catherine Ashton.
Iran and the five permanent members of the UN Security Council plus Germany haggled over details Wednesday on the second day of their final discussions, aiming to turn an interim accord reached a year ago into a lasting agreement before a November 24 deadline.