U.S. officials say Iran is being invited to participate for the first time in international talks aimed at peacefully ending Syria's four-year civil war.
The next diplomatic round starts Thursday in Vienna. Secretary of State John Kerry, Russian Foreign Minister Sergey Lavrov and several top European and Arab diplomats will attend.
The officials, who weren't authorized to speak on the record and demanded anonymity, said Russia delivered the invitation; Iran has yet to respond.
Washington had held out the possibility of Iran joining the discussions. But Syria's Western-backed opposition and U.S. allies, particularly Saudi Arabia, opposed such a move.
Iran has backed Syrian President Bashar Assad's government throughout the conflict, fighting alongside Syria's military. The U.S. and its allies support the opposition.
