Iran and world powers appeared close to a deal on Monday to give Tehran sanctions relief in exchange for limits on its nuclear program.
However, Iranian officials said talks could run past their latest midnight deadline. Iranian Foreign Minister Mohammad Javad Zarif was quoted as saying, "There shouldn't be any extension,but we can continue the talks as long as necessary."
Diplomats close to the talks said there were contingency plans for an announcement ceremony on Monday if the negotiators sealed an agreement.
That would open the door to ending sanctions that have crippled Iran's economy, in exchange for at least a decade of restrictions on its nuclear program.