LAUSANNE, Switzerland – Quiet talks on Lake Geneva between the US and Iran intensified markedly on Saturday, as the foreign ministers of Germany, France, and the EU arrived seeking an endgame on talks with Tehran over its nuclear program.

A common refrain was heard throughout the day: A deal is in sight, but gaps remain. Yet as the ministers arrived, each underscored that the moment was upon them to make historic decisions over how to proceed.

German Foreign Minister Frank-Walter Steinmeier told reporters that, in clear view of the Swiss Alps at a palace on the lake’s shore, he was reminded “that as one sees the cross on the summit, the final meters are the most difficult, but also the decisive ones.”

“The endgame of the long negotiations has begun,” Steinmeier said, before entering a meeting with French Foreign Minister Laurent Fabius and US Secretary of State John Kerry.

Fabius sounded more hopeful that a deal amenable to Paris was at hand. The French government has been publicly skeptical that a political framework agreement could be reached by Tuesday, a self-imposed deadline by world powers.

“Not enough” progress had been made yet on core issues – the pace of sanctions relief for Iran, the length of a deal or on the document itself – to announce a breakthrough, Fabius told the press in French.

And arriving at the back entrance of the palace at night, EU foreign policy chief Federica Mogherini declared the parties “never closer” to a nuclear agreement. Gaps remain, she added.

Negotiators have kept disciplined in their silence on the details of the issues outstanding, though some appear to be tactical: Whether a political framework should be oral or written, short or long, detailed or a mere “understanding” of the path forward.

Between marathon meetings incorporating their deputies, political directors, and technical and sanctions experts, Iranian Foreign Minister Mohammad Javad Zarif said he feared a two page framework deal would become a “paper tiger,” disposable in the months to come as the parties hammer out a comprehensive accord.

“In negotiations, both sides must show flexibility,” Zarif proclaimed on Twitter. “We have, and are ready to make a good deal for all. We await our counterparts’ readiness.”

US representatives remained quiet, noting only that the days to come are pivotal.

“It was important that ministers began to arrive for consultations, coordination, and negotiations today,” said one senior State Department official, after several rounds of meetings. “The serious but difficult work continues. We expect the pace to intensify as we assess if an understanding is possible.”

Kerry and Zarif met twice during the day, once with and once without their deputies. The foreign ministers of the United Kingdom, Russia, and China are to arrive in Lausanne on Sunday.

Security tightened around the palace as top diplomats began to arrive, along with massive staffs and press corps of their own. Media organizations have taken over a facility next to the Beau-Rivage Palace hotel, where the official museum of the Olympics is housed, as a filing center.

But both buildings would be too small to host an announcement of an agreement. Iran seeks to hold the event, should a deal be reached, at a neutral United Nations facility in nearby Geneva.

On Friday, British Foreign Secretary Phillip Hammond sounded an optimistic note, saying the parties could reach the “right deal” before the end of the month.

“We will not do a bad deal, but we are increasingly hopeful we may be able to do the right deal, which will ensure that Iran’s access to nuclear technology is channeled entirely for peaceful purposes,” he said.

Israel adamantly opposes of the agreement in its current form, and reiterated its displeasure on Saturday in various fora.

Earlier in the day, Prime Minister Benjamin Netanyahu received a call from Russian President Vladimir Putin congratulating him on his reelection as prime minister. They also discussed Iran.