VIENNA — Facing a stubborn demand from Iran, the United States and five other world powers have tentatively decided to adjourn their nuclear talks two days early but plan to extend the negotiations past a planned July 20 deadline, diplomats said Wednesday.

Both sides had been prepared to talk until Sunday, the informal deadline for the talks on Iran's suspected nuclear weapons program. But two diplomats have told The Associated Press the talks will probably wind down Friday, because the differences won't be bridged by Sunday.

The main dispute is over uranium enrichment, which can make both reactor fuel and the fissile core of nuclear warheads.

Up to last week Iran insisted on being allowed to expand its enrichment program over the next eight years to a level that would need about 190,000 current model centrifuges.

It now has about 20,000 centrifuges, with half of them operating. Iranian officials have recently signaled they are ready to freeze that number for now. But Kerry said Tuesday that Washington has made it "crystal clear" that even 10,000 are too many.

The diplomats demanded anonymity because they were not authorized to divulge confidential information. One said the two sides opposed going on until the final hours of the informal deadline because they felt that would give the impression they were desperate for a solution.

The talks aim at a deal that curbs Iran's suspected nuclear weapons programs in exchange for an end to the nuclear-related sanctions on Iran.

U.S. Secretary of State John Kerry spoke of "very real gaps" Tuesday after two days of meetings with Iranian Foreign Minister Mohammad Javad Zarif. White House spokesman Josh Earnest said that Kerry and President Barack Obama met Wednesday to discuss the "path forward" on the talks.

Russia, China, Britain, France and Germany are also participating.