MOSCOW (REUTERS) - Nuclear talks between Iran and six world powers have virtually stalled and a deadline for a final deal may have to be postponed again, Russian news agency Tass quoted a diplomatic source as saying on Friday.

Iran and the powers - the United States, Russia, China, France, Britain and Germany - reached a framework deal on April 2 in Switzerland and are seeking to strike a broader settlement by June 30 under which Iran would curb its nuclear programme in exchange for relief from economic sanctions.

The latest round of discussions in Vienna on Friday made no significant progress, the source from one of the missions said, according to Tass.

"The process has virtually stalled, there is risk that deadline will have to be postponed again," the source added.