Two days of marathon negotiations, by far the most direct and extended high-level contact between the United States and Iran in more than three decades, ended early Sunday without agreement on an interim plan on Iran’s disputed nuclear program.

After a tumultuous day of bargaining, diplomats emerged after midnight to acknowledge they had fallen short of a deal that would have required Iran to suspend key parts of its nuclear program in exchange for modest relief on economic sanctions. The sides will try again Nov. 20.

Secretary of State John F. Kerry, who had flown to Geneva at the eleventh hour to try to close a deal, said at a late-night news conference that the talks between Iran and six major powers had been “very productive” and that all sides were determined to continue the efforts.

“We came to Geneva to narrow the differences, and I can tell you without any reservations, we made significant progress,” Kerry said.

“It takes time to build confidence between countries that have really been at odds with each other for a long time now,” he said.

Although a deal had appeared nearly certain a few hours earlier, the talks stalled over technical issues, including details of nuclear concessions required of Iran, and the incentives the Islamic Republic would receive in return. Among the obstacles were disagreements between France and other members of the six-nation bloc known as the P5-plus-1.

Kerry, in a taped interview with NBC’s “Meet the Press,” that airs Sunday, downplayed the differences between Western governments that emerged on the final day of the talks. “A number of nations – not just the French, but ourselves and others – wanted to make sure that we had the tough language necessary, the clarity in the language necessary to be absolutely certain that we were doing the job and not granting more or doing something sloppily that could wind up with a mistake,” He said.

He forcefully rejected accusations that the deal offered to Iran would have endangered Israeli and other allies in the region by allowing Iran to retain some of its civilian nuclear capabilities. “We are not blind, and I don’t think we’re stupid,” Kerry said. “I think we have a pretty strong sense of how to measure whether or not we are acting in the interests of our country and of the globe, and particularly of our allies like Israel and Gulf states and others in the region.”

Kerry added: “We are absolutely determined that this would be a good deal, or there’ll be no deal. Now, that’s why it’s hard.”

Iran’s chief negotiator, Foreign Minister Mohammad Javid Zarif, gave an upbeat assessment as the talks broke up early Sunday.

“What I was looking for was the political determination, willingness and good faith and readiness in order to end this,” said Zarif, appearing at the podium with the European Union’s foreign policy chief, Catherine Ashton. “I think we’re all on the same wavelength, and that’s important. And that gives us the impetus to go forward when we meet again next time.

“We’ve done a lot of work. Hopefully we can do a bit more,” he said.

Ashton, reading a brief statement, said, “A lot of concrete progress has been achieved, but some differences remain.”

Ashton declined to characterize which of the six foreign ministers at the table across from Iran — representing the United States, Britain, France, Germany, Russia and China — had raised objections to the draft proposal. But reports from inside the closed meetings and public statements by the foreign ministers throughout the day indicated that France had been most adamant in refusing to agree to the proposal.

“There are still some questions to be addressed,” French Foreign Minister Laurent Fabius said as he left the final meeting.

Zarif declined to criticize the French. “Obviously the six countries may have differences of views,” he said, “but we are working together, and hopefully we will be able to reach an agreement when we meet again.”

The draft plan called for Iran to temporarily freeze key parts of its nuclear program that would enable it to quickly make nuclear weapon in the future if it chose to do so. But the plan reportedly did not require Iran to halt all uranium enrichment, though it did require a full dismantlement of a partially completed nuclear reactor that could, if finished, produce plutonium for nuclear weapons. The temporary freeze was to be an interim step to halt Iran’s nuclear progress as a more comprehensive deal was being negotiated.

The announcement concluded a day of musical chairs and closed sessions that went into Saturday night. As officials emerged from one meeting to begin another, they offered differing accounts of the progress being made.

Kerry met with Zarif and Ashton for five hours on Friday and two hours at midday Saturday before a third session that began well after dark.

Officials said that some of the strongest objections to the draft agreement that is the basis for the talks came from Fabius, who said the six nations should avoid falling for a “fool’s game” that was advantageous to Iran. Fabius was particularly concerned about Israel’s security, which he said must be taken “fully into account.” In a telephone call on Friday, President Obama tried to reassure Israeli Prime Minister Benjamin Netanyahu after he had called the draft “a very bad deal.”

“There is an initial draft that we do not accept,” Fabius told French radio, adding, “I have no certainty that we can finish up” before the departure of the foreign ministers who came to Geneva to lend weight to the talks.

British Foreign Secretary William Hague sounded somewhat more optimistic, telling reporters that the participants would continue “to apply all our efforts to this today to try to seize this opportunity.” Hague said officials were “conscious of the fact that some momentum has built up,” although “there is no fixed time for us to reach a conclusion.”

Both Fabius and Hague cited complications arising from the two main issues in the negotiations. Disagreements center on the status of Iran’s Arak heavy-water reactor and the separate production of highly enriched uranium — both processes that can be used to produce a nuclear weapon — and on what to do with the stockpile of uranium that Iran has already enriched to 20 percent.

Some supporters of a deal harshly criticized the French opposition to the proposed freeze.

“Blow number one against diplomacy today by the French,” tweeted Trita Parsi, president of the National Iranian American Council, a Washington-based grass-roots organization. “Next week, Congress will pass [new sanctions legislation against Iran]. Blow Number 2.”

Other arms-control advocates, while disappointed in the outcome, said they were encouraged the sides came as close as they did. Daryl Kimball, executive director of the Arms Control Association, said the negotiators’ obvious determination was a positive sign.

“A deal is clearly in the interest of both sides and would open the way for a more comprehensive, more permanent agreement that rolls back Iran’s overall enrichment capacity,” Kimball said. He said the differences between France and the other Western powers “can and should be resolved quickly.”

But others said the last-minute breakdown prevented what would have been a disastrous deal. Mark Dubowitz, director of the Foundation for Defense of Democracies, a Washington-based think tank, said French resistance “prevented an American collapse at the negotiation table.”

“The Obama administration, at the high water mark of its economic leverage, was ready to trade it all away for an interim deal that would have paved the way for an even worse final deal,” Dubowitz said.

Warrick reported from Washington.