U.S. Secretary of State John Kerry says key issues remain unresolved and important gaps need to be closed in the Iran nuclear talks. (Reuters)

U.S. officials were closed-mouthed Friday night about the status of a possible international deal over Iran’s disputed nuclear program, following a five-hour meeting here between Secretary of State John F. Kerry and Iranian Foreign Minister Mohammad Javad Zarif.

“We continued to make progress as we worked to narrow the gaps. There is more work to do,” a senior State Department official said of the session, which extended nearly until midnight. The official, speaking on the condition of anonymity to discuss the diplomatic talks, said “the meetings will resume” Saturday morning.

Kerry was joined in Geneva by his counterparts from Britain, France and Germany, which are also participating in the negotiations that began Thursday and were variously reported to be near agreement or hung up over what Kerry called “some very important issues . . . that are unresolved.”

The expected arrival here Saturday of Russian Foreign Minister Sergei Lavrov and China’s foreign minister or his deputy fueled optimism that the presence of a full complement of top diplomats from the six countries negotiating with Iran was the prelude to the announcement of a deal.

“Tomorrow we expect to attain a long-standing result that the whole world hopes for,” Russian Deputy Foreign Minister Sergei Ryabkov told the Ria Novosti news agency.

A senior member of Iran’s negotiating team, Deputy Foreign Minister Majid Takht Ravanchi, told reporters that “the text of the draft agreement has been prepared and initial negotiations” would take place in the Kerry-Zarif meeting, which was also attended by European Union foreign policy chief Catherine Ashton.

But Kerry, at least before his meeting with Zarif, seemed far less certain. “There is not an agreement,” he said on arrival in Geneva. Kerry said he and his colleagues were here to help “narrow some differences” rather than to finalize a deal.

An agreement was described by U.S. officials as a “first step” in a comprehensive pact restricting Tehran’s ability to seek atomic weapons.

Differences remained over the key issues of how much the United States and its negotiating partners were prepared to ease sanctions to provide Iran’s failing economy with cash, and the extent to which Iran was willing to freeze its reactor and uranium-enrichment programs.

Kerry expects to spend at least another day in Geneva, aides said, with current plans to leave Sunday for a previously scheduled trip to the United Arab Emirates. He has canceled planned stops in Algeria and Morocco to return to Washington for consultations and briefings with the White House, Congress and foreign partners.

Israel, in particular, remains staunchly opposed to any deal that does not require Iran to eliminate its uranium-enrichment centrifuges. On Friday, the government of Prime Minister Benjamin Netanyahu repeated its warning to negotiators that they should not back off their crippling sanctions until Iran’s entire nuclear program is eradicated.

In a reflection of the administration’s concern over Israeli complaints, President Obama called Netanyahu on Friday to give him an update on the Geneva negotiations, just hours after Kerry had delivered the same message in a meeting with Israeli leaders in Tel Aviv before departing for Geneva.

For the first time in 34 years, top elected officials in the U.S. and Iran are talking. Meanwhile, Americans are increasingly curious about Iran. The Washington Post’s Tehran Correspondent Jason Rezaian says daily life in Iran is a mix of traditional and modern. (Sarah Parnass/The Fold/The Washington Post)

Obama, the White House said, “underscored his strong commitment to preventing Iran from obtaining a nuclear weapon.”

While administration officials have not publicly revealed details of the freeze proposal offered to Iran, senior U.S. officials briefed on the plan say it suspends the parts of the program that could be used by Tehran to quickly assemble a nuclear weapon.

The plan would not, according to Iranian officials, require Iran to halt all uranium enrichment, or dismantle the centrifuges used by Iran to make the ­low-enriched nuclear fuel used in power plants. Israeli officials and many U.S. lawmakers have insisted on a halt to all uranium enrichment — something Iran says it will never agree to do.

Clifford Kupchan, a former State Department official and an Iran expert, said pressing for a full dismantlement of Iran’s uranium facilities would almost certainly have collapsed the negotiations while creating a rift in an international coalition that has supported financial sanctions until now.

“Any deal with an opponent is an ugly deal,” Kupchan said. “The enrichment train has left the station — Iran already enriches uranium and they will not roll that back. The choice then is between an ugly deal, a military conflict or tolerating a nuclear-capable Iran. That is a very easy choice.”

Current and former U.S. officials familiar with the broad outlines of the proposed deal said it included significant concessions by Iran, well beyond what many Iran observers believed was possible only a few months earlier. “It is a very strong proposal from our side,” said one former U.S. official who said he was briefed on some of the details.

Based on past negotiations, the remaining sticking points probably involve the amount of financial relief Iran would receive in return, said the official, who spoke on the condition of anonymity to discuss the confidential proposal. Iran had sought, unsuccessfully, for a rollback of the harshest sanctions on its oil and banking industries. But instead it is being offered a temporary, conditional rollback of some of the more modest sanctions, the official said.

Warrick reported from Washington.