Negotiators at the Iran nuclear talks plan to announce on Monday that they have reached agreement on a historic deal capping nearly a decade of diplomacy that would curb the country's atomic program in return for sanctions relief, diplomats told The Associated Press on Sunday.

The two diplomats said that a provisional agreement may be reached even earlier - by late Sunday. But they cautioned that final details of the pact were still being worked out and a formal agreement still awaits a review from the capitals of the seven nations at the talks.

And senior U.S. and Iranian officials suggested that not enough time was left to reach a provisional deal by Sunday. All of the officials, who are at the talks, demanded anonymity because they weren't authorized to discuss the negotiations publicly.

"We are working hard, but a deal tonight is simply logistically impossible," the Iranian official said, noting that the agreement will run roughly 100 pages.

The senior U.S. official declined to speculate as to the timing of any agreement or announcement and noted that "major issues remain to be resolved in these talks."

Movement toward a deal has been marked by years of tough negotiations. The current round in Vienna has run more than two weeks and blown through three deadlines.

Even before the envoys spoke to the AP, the nuclear negotiations appeared on the way to an agreement.

U.S. Secretary of State John Kerry, who on Thursday had threatened to walk away from the negotiations, noted Sunday that "a few tough things" remain in the way but added "we're getting to some real decisions."

En route to Mass at Vienna's gothic St. Stephens Cathedral, Kerry said twice he was "hopeful" after a "very good meeting" Saturday with Iranian Foreign Minister Mohammad Javad Zarif, who had Muslim services Friday. (Associated Press)

More From WBSM-AM/AM 1420