LAUSANNE, Switzerland — The United States and its negotiating partners on Tuesday extended their deadline for reaching a preliminary accord with Iran on its nuclear program until Wednesday.
But that one-day extension came with a White House warning that the Obama administration was prepared to step back from its diplomatic efforts if it concluded that the initial accord could not be reached.
"I actually would say that if we're not able to reach a political agreement in the timeline that we've described that we would walk away from the negotiating table," Josh Earnest, the White House spokesman, said Tuesday.
The Obama administration has approached the talks as a two-phase process. The preliminary accord it is trying to negotiate as a first step is intended to lay the foundation for a more detailed accord that would be fleshed out by the end of June.
The nations involved in the talks with Iran are Britain, China, France, Germany, Russia and the United States.
There have been signs that some of the most difficult issues will be deferred for a final agreement in three months.
But even getting that preliminary accord has been hard. The thorny issues have included disputes over what limits would be placed on the development of new types of centrifuges to enrich uranium and the pace for removing sanctions.
And on Monday the State Department acknowledged that a key question - the disposition of Iran's large stockpile of nuclear fuel -- also remained a subject of debate.
"The bottom line is that we don't have agreement with the Iranians on the stockpile issue," said Marie Harf, a State Department spokeswoman.
But the talks have also been burdened by clashing negotiating strategies.
The Obama administration wants to nail down specific limits on Iran's nuclear program as soon as possible so that it can better resist moves in Congress to impose additional sanctions.
It also wants any sanctions relief to be gradual in order to ensure that it does not come before Iran meets its obligations under a nuclear accord.
Frank-Walter Steinmeier, the German foreign minister, reinforced the sense of progress when he said Friday morning that the talks had been in something of a crisis but that negotiators seemed to have settled on "a bit of a new approach."
As the day dragged on, however, a European official said that the talks were difficult. By early evening, the Tuesday deadline had been extended.
"We've made enough progress in the last days to merit staying until Wednesday," Harf said. "There are several difficult issues still remaining."
U.S. officials said that no ultimatums had been issued. But with lawmakers set to return in mid-April after a congressional recess, Earnest signaled that there was only so long that the White House was prepared to wait.
"If we are making progress toward the finish line, then we should keep going," he said. "If we're not able to reach a political agreement, then we're not going to wait all the way until June 30th to walk away."