LAUSANNE, Switzerland -- Sunset fell on a deadline with Iran over its nuclear program with no agreement among diplomats gathered here in the Swiss Alps, working through the night unclear on the path forward.
US negotiators said they would continue sleeplessly into the morning hours in order to hammer out a political framework with Iran, which they hope will address all major elements of a comprehensive accord ending concerns with Iran's decades-old nuclear program.
The deadline for a far-reaching deal is June 30. But the Obama administration is willing to walk away from the talks before then, White House press secretary Josh Earnest told reporters in Washington, if Iran is not prepared to make the necessary political decisions in the hours to come.
"If we have made progress toward the finish line," Earnest added, "then we should keep going."
Tea leaves early in the day of their deadline, March 31, suggested talks may continue past midnight. Germany's Foreign Minister Frank-Walter Steinmeier began telling local press that the talks were in "a bit of a crisis." He did not elaborate.
Early in the afternoon, US officials began suggesting the talks may continue into April 1 "if it's useful to do so." They committed for the night later on, as planes sat idle on Geneva runways for the American and Chinese delegations.
And as the clock struck 9 p.m. in Lausanne, where the effort continued for a fifth day, envoys appeared weary in the halls of the Beau Rivage Palace. European High Representative Federica Mogherini rubbed tired eyes; US Secretary of State John Kerry told journalists, "we're working hard," off for short respite at a restaurant in the hotel.
"We've made enough progress in the last days to merit staying until Wednesday," State Department Acting Spokesperson Marie Harf said as the night dwindled without a deal. "There are several difficult issues still remaining."
Chinese Foreign Minister Wang Yi took his flight as scheduled and left the talks on Tuesday night, leaving his deputy to continue in his place, as French Foreign Minister Laurent Fabius described the negotiations as complicated, long and difficult.
"I fear that we will spend the night," Fabius told reporters here.
"The mood is back and forth— a difficult struggle for a realistic solution that is acceptable to both sides," one German delegate said. "It remains an open question whether we will succeed."
Obama administration officials said leading up to the deadline that, without agreement, Washington would have to reassess the path forward. This week was "time to make hard decisions," Kerry told the press last week, entering the latest round of a two-year negotiation.
The US, Britain, France, China, Russia and Germany seek to cap, restrict, monitor and partially roll back Iran's nuclear program for a finite period.
But gaps remain on some of the largest issues in reaching an understanding on how to get there.
Protecting its veto influence at the United Nations, Russia is fighting a US-designed mechanism with which the UN Security Council could "snap back" sanctions on Iran after voting for their repeal, without going through the process of a second vote. Moscow warns that such a mechanism undermines the authority of the chamber's permanent members, setting a dangerous precedent.
Earlier in the day, before departing Moscow for Lausanne, Russian Foreign Minister Sergey Lavrov called for the swift lifting of sanctions on Iran and said that a deal was in clear sight should the West agree.
But Paris has opposing concerns. The French government wants sanctions on Iran to last far longer than Iran is willing to tolerate, their easing tied strictly to actions from Tehran that permanently roll back its nuclear capacity.
Beyond the political concerns over quickly lifting sanctions on Iran at the UN, negotiators are still wrestling with the technical challenge of monitoring Iran's research and development into nuclear various technologies.
Nor have world powers settled with Iran how best to handle its existing stockpile of enriched uranium. Negotiators have not even reached a tentative agreement on that matter, US officials said on Tuesday, after Iran renewed its rejection of removing its stockpile to Russia for conversion.
"Negotiations are continually broken off for discussions in smaller circles," the German diplomat continued. "Still to early to think about stopping the clock, but may perhaps prove necessary."
Speaking to his own press corps, Hamid Baeidinejad, one of Iran's negotiators, said that the permanent five members of the United Nations Security Council "need more coordination" entering the final hours of talks. Several Iranian outlets are reporting disagreement even within the country-specific delegations, particularly the French.