LAUSANNE, Switzerland -- If U.S. negotiators are ultimately able to conclude a "political understanding" with Iran on its nuclear program, as they said they were striving to do Thursday morning, the seeds might have been planted earlier in the week.
With only hours to go on Tuesday night before the end-of-the-month deadline that had been set by the White House, Secretary of State John Kerry and Energy Secretary Ernest J. Moniz stepped into a large tent erected in a luxury hotel here and dialed into a video conference with President Barack Obama.
There was no way to meet the deadline, Kerry said from the tent, which was designed to defeat eavesdropping. The Iranians, he said, perhaps sensing that the deadline meant a lot in Washington and little in Tehran, were intransigent.
"They were turning our own deadline against us to see if we would give ground," just to be able to claim that the March 31 date had been met, said one senior official, who would not be named because of the secrecy surrounding the talks.
Obama, according to two people familiar with the discussion, told Kerry and Moniz to ignore the deadline, make it clear that the president was ready to walk away and leave all sanctions on Iran in place, and see if that would change the dynamic.
It is still not clear if the last-minute change in tactics will succeed in convincing the Iranians that the Obama administration does not want the accord more than they do, or yield a different result.
But it was an example of the negotiating gamesmanship that has taken over the talks here. Kerry has kept his plane warmed up. Foreign ministers who came to sign an accord have returned home for other duties. France's top diplomat, Laurent Fabius, tieless, came up in the elevator on Wednesday night musing to his aides that he had been there just a day before.
Kerry spent Wednesday night meeting again with his Iranian counterpart, Mohammad Javad Zarif, for what diplomats said could be a series of pivotal sessions. At issue, officials said, were the pace at which sanctions would be lifted and restrictions on Iran's ability to develop new, advanced centrifuges, which are over 20 times more powerful than its current models.
Heading toward the meetings, Zarif repeated an oft-used talking point, insisting that Iran was showing flexibility and that it was up to the U.S. and its partners to reciprocate.
"Our friends need to decide whether they want to be with Iran based on respect or whether they want to continue based on pressure," Zarif said. "They have tested the other one; it is high time to test this one."
For weeks, critics complained that the March 31 deadline the Obama administration had set for a preliminary accord might backfire by adding to the pressure on U.S. negotiators to make last-minute concessions.
The Obama administration has an eye to selling the agreement to a skeptical Congress. But winning the battle with Congress, the critics said, will depend more on what concrete agreements are reached here, and what issues are put off for further talks with the Iranians, than on whether a preliminary accord is settled on Wednesday or over the next week or two. And as French diplomats have repeatedly pointed out, the deadline for wrapping up a final, detailed accord is not until the end of June.
Obama's decision Tuesday night to ignore the deadline he had set for himself was intended to persuade the Iranian leadership, watching these sessions from Tehran, to think twice about the hardnose brinkmanship Iran negotiators had exhibited in previous rounds of talks.
Germany's foreign minister, Frank-Walter Steinmeier, said before the meetings Wednesday night that the Iranians were expected to present "new recommendations" on how to bridge the gaps that have been holding up the accord.
"Naturally, whoever negotiates has to accept the risk of collapse," said Steinmeier, who made it clear he was staying for another day. "But I say that in light of the convergence that we have achieved here in Switzerland, in Lausanne, it would be irresponsible to ignore the possibility of reaching an agreement."
Marie Harf, a State Department spokeswoman, confirmed that Kerry had decided to stay on to give diplomacy another try.
"We continue to make progress but have not reached a political understanding," she said. "Therefore, Secretary Kerry will remain in Lausanne until at least Thursday morning to continue the negotiations."
The talks have been snarled by disagreements over what sort of research should be permitted on advanced centrifuges to enrich uranium; the pace of the lifting of sanctions, especially those imposed by the United Nations; and other issues. Another matter in dispute has been whether a preliminary accord should lay out specific limits, as the United States has insisted, or be more general, as Iran has preferred.
As the sense of momentum built, news came that Philip Hammond, the British foreign secretary, was also returning here Thursday morning.
"We are a few meters from the finishing line, but it's always the last meters that are the most difficult," Fabius told reporters in his most optimistic comments to date. "We will try and cross them."
Jodi Rudoren contributed reporting from Jerusalem.