Another day passed at the Iran nuclear talks Friday, ending the same way as the 13 days preceding it, as officials reported progress — but no deal.

A senior U.S. official said the talks were being extended through Monday, keeping in place an interim agreement while negotiations continue. The extension is the third since an original deadline of June 30 passed without a final agreement between a six-nation group trying to get Iran to accept long-term restrictions on and monitoring of its nuclear program in exchange for sanctions relief.

“I think we have resolved some of the things that were outstanding, and we’ve made some progress,” Secretary of State John F. Kerry said.

The diplomats here dwindled down to a core group from Iran, the United States and Germany as the foreign ministers of France and Britain left Friday. Their counterparts from Russia and China left Vienna several days ago. Most are expected to return Saturday or Sunday.

Before leaving, British Foreign Secretary Philip Hammond called progress “painstakingly slow.”

Kerry and Iranian Foreign Minister Mohammad Javad Zarif met again Friday, a day after Kerry warned that the United States was prepared to walk away from the talks and a few hours after Zarif emerged from a Vienna mosque and accused the United States and the Europeans of backtracking.

“Unfortunately, we have seen changes in the position and excessive demands . . . by several countries,” Zarif said.

A bone-weary humor ruled the day, as one diplomat from the European Union joked about jumping off the balcony of the swank Coburg Palace hotel, where the talks are being conducted.

Zarif, when asked whether the negotiators would still be in Vienna on Monday, replied with a sigh, “I hope not.”

While a deal could be finalized at any time, the extension suggests that the tortuous negotiations will continue throughout the third weekend in the Austrian capital since Kerry and Zarif arrived on June 26, expecting to complete their task in four days or so.

The talks have been deadlocked on a handful of issues. One major point is whether the United States will soften its opposition to the lifting of a U.N. embargo on sales of conventional arms to Iran. Moscow and Beijing support Iran on the issue, and Russian President Vladimir Putin on Friday called for the embargo to be lifted as soon as possible.

Although Kerry on Thursday cautioned that the United States will not stick around indefinitely, the costs of walking away would be high, even if the talks were to resume later. Virtually every time there has been a break during a year and a half of negotiations, administration officials have said, the talks have resumed with Iran backtracking — as it now accuses the United States and the Europeans of doing.

Already, the delay is prolonging debate in Washington. The administration had hoped to have already wrapped things up, allowing it to submit a final deal to Congress for a 30-day review. Now the review period is automatically extended to 60 days, allowing critics of the deal more time to build opposition.

In Tehran, Parliament Speaker Ali Larijani issued a direct warning to the United States and its negotiators.

“If you drive the talks into a dead end, then it will be you who will be committing a strategic mistake,” he said at Friday prayers. “And its outcome will not benefit you since Iran’s nuclear staff are ready to accelerate nuclear technology at a higher speed than before.”

U.S. officials have said they will keep talking so long as they believe they can achieve something. But both sides have cautioned that there is no partial deal.

“I think everyone understands that once we leave here, we are in less control of what happens in this negotiation,” a senior administration official said this week, speaking on the condition of anonymity. “It gets more complicated, not less complicated. That puts pressure on all of us to make the best use of the time and to try to really punch through or find out we can’t.

“And sometimes things have to align in history, at a moment in history, to be able to do something.”