Iran and six world powers extended their negotiations on a nuclear deal for yet another day Wednesday, agreeing to resume talks Thursday as Iran called on the global powers to "seize the moment and use this opportunity which may not be repeated."
Marie Harf, the State Department's acting spokeswoman, said Secretary of State John Kerry would remain in Lausanne, Switzerland, for at least another day because "we continue to make progress but have not reached a political understanding."
Top diplomats from Iran and the P5+1 — the U.S., Britain, China, France, Germany and Russia — have worked well past their midnight Tuesday deadline to agree on a framework for a final accord that would limit Iran's nuclear program, which they hope to sign by the end of June.
The foreign ministers of Britain and France, who had already left the talks, were on their way back to Lausanne, officials told NBC News, lending support to the prospect that an agreement might be announced.
In dispute has been the form of any statement: Iran does not want one to be particularly specific, while the U.S. and the others want a more detailed document that could help the Obama administration defend the deal to Congress.
Kerry had two one-on-one meetings Wednesday with Iranian Foreign Minister Javad Zarif, who indicated that the world powers might see more progress if they took their foot off the gas a little bit. One meeting was about 10 minutes, and the other was about 30. Meetings were planned into the night.
Under pressure from the P5+1 to compromise, Zarif reiterated that Iran views sanctions, a key sticking point, as "pressure."
"I've always said that an agreement and pressure do not go together. They are mutually exclusive," Zarif told reporters after meeting with Kerry. "So our friends need to decide whether they want to be with Iran based on respect or whether they want to continue based on pressure. They have tested the other one. It is high time to test this one."
Zarif noted that the window for a resolution was closing and said: "Iran has shown its readiness to engage with dignity, and it's time for our negotiating partners to seize the moment and use this opportunity which may not be repeated."
But White House press secretary Josh Earnest told reporters in Washington that the U.S. wouldn't be manipulated into making concessions to bring Tehran to an agreement, saying the U.S. was prepared to walk away if it can't get a good deal.
"The talks continue to be productive, and progress is being made," Earnest said, but "these negotiations are not open-ended."
German Foreign Minister Frank-Walter Steinmeier said negotiators were still facing a "tough struggle."
But he also said there were grounds for optimism, telling reporters that the world powers had presented detailed new proposals that "could lead to consensus" and were waiting for Iran to address them and make a commitment.
"I can't predict whether that will be sufficient to reach an agreement in the course of the night," Steinmeier said. "Accuracy is more important than speed, [but] I am of the opinion that a success is still possible."
— Andrea Mitchell and M. Alex Johnson