Iranian negotiators left Rome persuaded that the U.S. had accepted Tehran's position that it would not entirely end its enrichment programme or surrender all the uranium it has enriched already, but that its missile programme remained a big sticking point, the official said.

Iran and the U.S. began talks in Oman on Saturday over Tehran's advancing nuclear program, as U.S. President Donald Trump threatens airstrikes if a deal is not reached.

Iran and the United States began in-depth negotiations in Oman over Tehran's rapidly advancing nuclear program on Saturday, talks that likely will hinge on the Islamic Republic's enrichment of uranium.