The United States said Wednesday that Iran’s adherence to an interim nuclear deal had been “surprisingly favorable,” as it contemplated a likely extension to talks on framing a final agreement.

US Secretary of State John Kerry was briefing President Barack Obama on the talks between world powers and the Islamic republic in Vienna, amid clear signs the process will go on after a Sunday deadline.

Kerry returned to Washington from the talks in Vienna late Tuesday, and is likely also to discuss any possible US mediation efforts in the conflict between Hamas and Israel in Gaza.

Kerry said before leaving Vienna that he would discuss with Obama “the prospects for a comprehensive agreement, as well as a path forward if we do not achieve one by the 20th of July, including the question of whether or not more time is warranted.”

He said after two days of talks with Iranian Foreign Minister Mohammad Javad Zarif that there had been “tangible progress on key issues” but “very real gaps” remain.

White House spokesman Josh Earnest appeared to prepare the political ground for an extension of the dialogue.

“It is clear that their track record over the last six months, I think many people would acknowledge, has been surprisingly favorable and that there has been a legitimate discussion and constructive engagement between Iran and the P-5 plus one,” Earnest said.

“There were a lot of people who were pretty skeptical about that six months ago.”

An interim accord on Iran’s nuclear program was struck in November between Tehran and the five permanent members of the UN Security Council plus Germany. It expires on July 20.

The deal froze aspects of Iran’s nuclear program in exchange for a slight easing of some of the sanctions that have crippled the Iranian economy.

An unnamed member of Iran’s delegation in Vienna told the official IRNA news agency that the current round of talks would finish on Friday.

“Negotiations between Iran and the P5+1 group will be extended by several months to continue working on the draft of a comprehensive agreement,” he said, but added that the extension was yet to be finalized.

The White House would not comment on reports an extension had already been agreed.

Iran denies seeking the atomic bomb and wants the lifting of crippling UN and Western sanctions.

The six powers want Iran to dramatically reduce the scope of its nuclear program for a lengthy period of time and agree to more intrusive UN inspections.

This would greatly expand the time needed for the Islamic republic to develop a nuclear weapon, should it choose to do so, while giving the world ample warning of any such “breakout” push.

Iran wants to expand its nuclear facilities, insisting they are for purely peaceful purposes and that it has the perfect right to nuclear activities under international treaties.

While on the road in Europe and Afghanistan, Kerry has conducted intense telephone diplomacy with Israeli Prime Minister Benjamin Netanyahu and US allies in the Middle East.

But he opted against an immediate personal mediation mission in the Middle East.