The UK said on Friday that a deal on reviving the 2015 accord between Tehran and world powers on Iran's nuclear program is "close", in Vienna negotiations.

"We are close. E3 negotiators leaving Vienna briefly to update ministers on state of play," British diplomat Stephanie Al-Qaq said on Twitter, referring to negotiators from Britain, France and Germany.

Along with counterparts from China, Iran and Russia they have been taking part in the latest round of talks in the Austrian capital since late November.

The U.S. has been participating indirectly.

Also on Friday, Iran's Foreign Minister Hossein Amir-Abdollahian said he was prepared to travel to Vienna if a deal is reached to revive the accord.