French Foreign Minister Laurent Fabius, US Secretary of State John Kerry, former EU foreign policy chief Catherine Ashton, the High Representative of the Union for Foreign Affairs, Britain's Foreign Secretary Philip Hammond and German Foreign Minister Frank-Walter Steinmeier meet for dinner at the residence of British ambassador in Vienna on November 23, 2014. At stake in the Austrian capital Vienna is a historic deal in which Iran would curb its nuclear activities in exchange for broad relief from years of heavy international economic sanctions. It could end a 12-year standoff with the West that has even raised the threat of Israeli military strikes against Iranian nuclear facilities. AFP PHOTO / POOL / JOE KLAMARJOE KLAMAR/AFP/Getty Images
What to know about the U.S.-Iran nuclear negotations
01:44 - Source: CNN
Lausanne, Switzerland CNN  — 

Nuclear talks reached a critical point Saturday as the ministers of France and Germany arrived to push a framework agreement with Iran ahead of Tuesday’s deadline.

The talks hit a snag as the negotiations entered their third day, with Iran standing firm on several sticking points that could jeopardize a deal, senior U.S. officials and Western diplomats said.

The sources said Iran has refused to budge on key issues centering around the scope of advanced nuclear research that Iran could continue to do while a deal is in effect, as well as the pace of sanctions relief.

“The Iranians are being very tough on the most difficult issues,” a senior U.S. official told CNN. “We are headed toward the deadline, so in some ways we expect this, but we really don’t know if we will get there.”

One Western diplomat surmised that the Iranian delegation faced pressure after returning home to Tehran following the last round of talks and returned with a harder negotiating position.

“We spent all of yesterday pushing the Iranians,” the diplomat told CNN. “They are not moving. It’s very difficult. It is not going well. We are really at a point where the Iranians need to decide whether they want this or not.”

Iranian Foreign Minister Javad Zarif tried to downplay tensions after meeting with French Foreign Minister Laurent Fabius and German Foreign Minister Frank-Walter Steinmeier, saying that some progress was made

“We are moving forward. I think we can in fact make the necessary progress to be able to resolve all of the issues and start writing them down in a text that will be come the final agreement,” Zarif said.

But suggesting the issue of sanctions remains a stumbling block, he added, “I believe they have realized that sanctions, pressure and an agreement will not go together. It’s only to translate that understanding and realization into the agreement that we are negotiating.”

Zarif meet Saturday with Secretary of State John Kerry. But U.S. officials said they hoped the arrivals of the other ministers in the negotiations would show unity among the parties and put pressure on the Iranians to sign onto a political framework pact that places curbs on Iran’s nuclear program ahead of the March 31 deadline.

British Foreign Secretary Philip Hammond and Chinese Foreign Minister Wang Yi also are expected this weekend

Kerry held several hours of talks with Iran on Friday, which the United States described as “tough and very serious.” The talks ended with the U.S. putting the responsibility on Iran to make compromises in order to reach agreement.

“We’re at that point in the negotiations where we really need to see decisions being made. We will test whether that is truly possible over the next several days,” a senior U.S. official told reporters.

But Iranians pushed back on the notion that it was up to them to bridge the last gaps that remain between them and the world powers with whom they are negotiating.

“Iran has made a decision, a political decision to go for engagement with dignity. I believe our negotiation partners also need to make this decision,” Zarif said Saturday.

Arriving at the Beau Rivage Hotel, where the talks are being held, French Foreign Minister Fabius said he wanted to see a “robust agreement.”

“Iran has the right to have civil nuclear program but not an atomic bomb,” Fabius said, adding that he will “insist on transparency and monitoring mechanisms to ensure the commitments taken are respected.”

German Foreign Minister Steinmeier said the talks had reached the “endgame, comparing the quest for a nuclear deal to trying to scale a peak in the surrounding Swiss Alps.

“As one sees the cross on the summit, the final meters are the most difficult but also the decisive ones. That’s what has to be done here in the coming hours and days,” he said. I can only hope that in view of what has been achieved over the last 12 months that the attempt for a final agreement here will not be abandoned.”

He added that a successful conclusion of the nuclear talks with Iran “could perhaps bring a bit more calm to the region.

Obama, Merkel agree ball is in Iran’s court

On Friday, President Barack Obama and German Chancellor Angela Merkel talked by phone and agreed that “Iran must make the decisions necessary to resolve the remaining issues,” according to a statement.

The comments were in contrast to the international negotiators’ optimism at the start of the talks that a framework deal would by struck by the deadline.

But even if a pact is reached, it is unclear what form it would take. A comprehensive deal including technical annexes is supposed to be concluded by June 30.

The U.S. wants the framework to be a formal written document, one that quantifies Iran’s commitments, to submit to Congress – an effort to prevent lawmakers from imposing additional sanctions on Tehran and prompting Iran to withdraw from the talks.

But U.S. and Western diplomats say the Iranian foreign minister is reluctant to sign an initial document out of concern revealing too many details could give an opportunity to hardliners who may try to scuttle a deal. Iran, Zarif has said, is looking simply for an “understanding” of what has been agreed to before a formal accord is reached.

“We do not know what form this will take if we can get there at the end of March,” a senior State Department official said. “The goal is to get as many specifics nailed down both with the Iranians and whatever we can say publicly.”