A senior U.S. official said Iran nuclear negotiations will go past the June 30 deadline.
"We've said that these talks could go beyond June 30th for a few days if we need some additional time," the official told reporters on condition of anonymity on June 28.
U.S. Secretary of State John Kerry and the foreign ministers of Iran, Britain, France, and Germany are attending the Vienna talks, along with officials from China and Russia.
The goal of the talks is an agreement under which Tehran would curb its nuclear program in exchange for sanctions relief.
The six powers want limits on Tehran's programs that could have a military use. Tehran denies it is pursuing such weapons.
Iranian media reported that Foreign Minister Mohammad Javad Zarif would return to Tehran later on June 28 for consultation.
The U.S. official said Washington wasn't concerned about Zarif decision to return to Tehran overnight, saying it was always expected that ministers would come and go from Vienna as the nuclear talks heated up.