Iranian Foreign Minister Javad Zarif, right, and the head of the Iranian Atomic Energy Organization Ali Akbar Salehi, third from right, confer following a meeting with U.S. Secretary of State John Kerry and other U.S. officials in Lausanne, Switzerland, Friday, March 27, 2015. (Brendan Smialowski/AP)

The United States and Iran forged ahead Friday in a bid to settle disagreements on Iran’s nuclear program, as diplomats from other countries involved in the negotiations made tentative plans to come to Lausanne ahead of a Tuesday deadline for a deal.

Secretary of State John F. Kerry and Energy Secretary Ernest Moniz met throughout the day with their Iranian counterparts, Foreign Minister Mohammad Javad Zarif and Ali Akbar Salehi, chief of Iran’s atomic energy agency. They ignored questions from reporters about whether they were close to an agreement. Helga Schmid, the deputy foreign policy chief for the European Union, also joined the talks.

The pressure on them is acute, because they have vowed to come up with a broad agreement by midnight Tuesday in Lausanne (7 p.m. Eastern time). Any agreement would outline the general “framework” of a deal, leaving many details to be worked out by the time an interim agreement expires at the end of June.

[A framework? A deal? The semantics of the talks]

Even as the negotiators were meeting in a five-star hotel on Lake Geneva, foreign ministers from the five other countries involved in talks with Iran were starting to make plans to join the discussions in the final days before Tuesday’s deadline. The looming deadline suggests that they may be coming to help with some remaining roadblocks.

Graphic: Iran's potential nuclear capability

The first to arrive apparently will be French Foreign Minister Laurent Fabius. Before leaving for Lausanne, he told reporters at the U.N. headquarters in New York on Friday that “more progress” was needed.

“The important thing is the content, not the deadline,” he said. “There has been some progress, but there are things which are not yet solved.”

British Foreign Secretary Philip Hammond’s office said he is expected to come to Lausanne this weekend. Hammond said Friday that “better than half” of the key issues in the negotiations are close enough to resolution “that we are sure we can reach agreement.”

Other issues “are going to require a significant move by the Iranians to reach our red line,” he told reporters during a brief visit to Washington.

German Foreign Minister Frank-Walter Steinmeier also may travel to the talks this weekend, “but no decision has been made yet,” his spokesman said.

The Russian news agency RIA Novosti said Foreign Minister Sergei Lavrov may arrive Sunday evening. It is not known whether China’s foreign minister, Wang Yi, will be coming.

Since this round of talks began in earnest almost 1 1 /2 years ago, the negotiators have talked up to the deadlines and beyond, only to conclude by announcing an extension of the interim agreement and a new deadline. President Obama has said there will be no extension this time, although failure to reach an agreement leaves the interim deal intact for three months. If there is no deal, it would be up to Obama to decide what steps to take next.

The talks are snagged over a number of fundamental “gaps,” including how much nuclear research and development Iran would be permitted and the pace at which international sanctions against it could be lifted.

Iran wants to continue research so it can modernize its uranium-enriching centrifuges, which use 1970s technology. It insists that its nuclear program is for civilian purposes alone, and its leaders say Islam forbids them from building nuclear weapons.

Iran also wants to see sanctions eased and lifted fairly swiftly. The United States and its negotiating partners are holding out for a gradual easing of sanctions, linked to the pace at which Iran allows international inspections of its uranium facilities, mines and mills, and otherwise complies with an agreement.

Kerry wants to return to Washington with an agreement that the administration can defend before skeptics in Congress, showing that the considerable effort his office has exerted in the talks produced a long-lasting, verifiable deal to ensure that Iran does not build nuclear weapons.

The United States is adamant that any deal provide a one-year “breakout” time, meaning that, through limitations and open inspections, the agreement ensures that it would take at least a full year for Iran to amass enough weapons-grade materials to build a bomb. Many factors go into that, including the number and efficiency of centrifuges, and negotiators say any compromise on one factor requires an offset elsewhere.

Any deal is expected to last for at least 10 years, although the French want a longer time frame. French diplomats have said that they would prefer to keep negotiating even if they do not have an agreement by Tuesday.

Karen DeYoung in Washington contributed to this report.

Read more:

Iran isn’t providing needed access or information, nuclear watchdog says

Israel seeks an ally in France to oppose Iran deal

Officials: U.S. considers letting Iran run nuclear centrifuges at fortified underground bunker

Eager investors await open door to Iran