EU High Representative for Foreign Affairs Catherine Ashton, right, walks next to Iranian Foreign Minister Mohammed Javad Zarif prior to the start of two days of closed-door nuclear talks at the United Nations offices in Geneva. (Martial Trezzini/AP)

A deal that would give Iran limited relief from economic sanctions in exchange for a temporary freeze of some of its nuclear activities was near completion late Thursday, and Secretary of State John F. Kerry was preparing to fly to Geneva Friday morning for a likely announcement.

Kerry, who has been traveling in the Middle East for the past week, will hold a trilateral meeting with Iranian Foreign Minister Mohammad Javad Zarif and European Union foreign policy chief Catherine Ashton to “help narrow the differences, “ according to Kerry spokeswoman Jen Psaki, who said that Ashton had asked him to come. A senior State Department official, speaking on condition of anonymity about the fast-moving events, said that Kerry has been open to joining the Geneva talks since they began last month if his presence was helpful.

French Foreign Minister Laurent Fabius also plans to travel to Geneva, according to official sources quoted by Agence France Presse. Other P5+1 governments have not yet indicated whether their foreign ministers will attend for the announcement of the phased plan, which would include the most significant restrictions on Iran’s nuclear facilities in nearly a decade.

An agreement, which U.S. officials described as a “first step” in a comprehensive pact restricting Tehran’s ability to seek atomic weapons, could herald a significant shift in U.S.-Iranian relations after years of enmity.

In the midst of a round of shuttle diplomacy between Israel and the Palestinians, Kerry spent Thursday night in Amman, Jordan, where he met with Palestinian President Mahmoud Abbas. En route to Geneva Friday morning, he stopped at Ben Gurion Airport in Tel Aviv for a third meeting in as many days with Israeli Prime Minister Benjamin Netanyahu.

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)

In an interview with The Washington Post on Thursday, Netanyahu blasted the U.S.-backed proposal as “a monumental mistake.”

“There’s no earthly reason to do this,” he said. “Not only the force of the existing sanctions but the threat of the future sanctions was the great impetus on the mind of Khamenei, and now they could just take that away.” He was referring to Ayatollah Ali Khamenei, Iran’s supreme leader, who holds ultimate political and religious authority in the country.

Speaking to reporters Friday morning before his meeting with Kerry, Netanyahu said he understood “the Iranians are walking around very satisfied in Geneva, as well they should be, because they got everything and paid nothing. Everything they wanted. They wanted relief of sanctions after years of a grueling sanctions regime. They got that. They are paying nothing because they are not reducing in any way their nuclear enrichment capability . . . Israel,” he said, “is not obliged by this agreement, and Israel will do everything it needs to defend itself and the security of its people.”

President Obama said in an interview with NBC News on Thursday that a phased agreement would help the United States monitor whether Iran has stopped developing nuclear weapons in return for a “very modest relief.”

“The best way to assure ourselves that Iran’s not getting a nuclear weapon is if we’ve got a verifiable means that they . . . are dismantling that program and international organizations can see what they’re doing and we can see what they’re doing,” he said.

U.S. officials said the proposed nuclear freeze, if accepted by Iran, would be the first stage in a multi-step process that could culminate in an agreement early next year on permanent limits to Iran’s ability to produce the components of a nuclear bomb.

The easing of sanctions would be reversed if Iran did not honor its commitments, or if it was unable to reach a broader nuclear agreement. The officials stressed that the toughest sanctions affecting Iran’s banking sector and oil exports would not be lifted until the final stage of the process.

Although Iran has not responded publicly to the freeze plan, its chief negotiator said the sides were “making progress,” while acknowledging that the discussions were “tough.”

“I believe it is possible to reach an understanding or an agreement before we close these negotiations tomorrow evening,” Iran’s Zarif told CNN.

White House spokesman Jay Carney said Thursday that any interim agreement would “address Iran’s most advanced nuclear activities, increase transparency so Iran will not be able to use the cover of talks to advance its program, and create time and space as we negotiate a comprehensive agreement.”

In a sign of progress, U.S. and Iranian diplomats held separate talks Thursday afternoon that lasted nearly an hour, a senior State Department official said. It was the second such bilateral meeting since the nuclear negotiations resumed three weeks ago.

“It was a substantive and serious conversation,” the official said of the talks between U.S. delegation leader Wendy Sherman and Iranian Deputy Foreign Minister Seyed Abbas Araghchi.

As the negotiations recessed for the night, Zarif and Ashtonagreed to meet early Friday to “work through some issues,” Ashton spokesman Michael Mann said.

Although many details are unclear, a senior U.S. official said the freeze proposal would include a suspension of nuclear activities and other restrictions in return for “limited, targeted and reversible” easing of some financial sanctions. But Zarif, in the CNN interview, suggested that a deal would allow some production of nuclear reactor fuel and would include recognition of Iran’s right to peaceful nuclear energy.

“There won’t be a suspension of our enrichment program in its entirety,” he told CNN’s Christiane Amanpour.

The prospect that Iran could be granted even partial relief from sanctions brought protests from Saudi officials as well as Israel’s conservative-led government, and Israeli officials attacked the Geneva proposal as seriously flawed.

“I think it’s a monumental mistake — a monumental mistake,” Netanyahu said in the interview.

The Israeli leader said the Iranians “of course” want nuclear weapons, and he vowed to oppose any deal that would ease pressure on Iran or allow it to preserve the ability to enrich uranium. Iran has insisted that it has a right to make low-enriched uranium used in nuclear power plants.

Kerry strongly defended the idea of a freeze, saying it would offer a way to stop Iran’s advances while lowering the risk of war. In an interview with an Israeli journalist, Kerry insisted that the Obama administration would neither accept a bad deal nor tolerate a nuclear-armed Iran.

“Let me just ask you simply: Are we better off not talking to them, and they continue to build the capacity, and then we have an automatic military confrontation?” Kerry said. “Or are we better off having a freeze where they are today and take the program backward so that you expand the amount of time before they could break out? Which way is safer? It’s very clear to me how you’re safer.”

In Tehran, Iranian officials appeared to be preparing the public for a possible nuclear deal. In a show of unity, a range of Iranian leaders — including prominent skeptics of an accord with the West — voiced support for diplomatic efforts.

“We do not need any criticism today, and any discussion in the country about the talks must be in the form of suggestions,” Hassan Ghashghavi, a deputy foreign minister, said Wednesday. “We already have a lot of criticism and are thirsty for suggestions and ideas.”

Sadegh Larijani, the conservative head of Iran’s judiciary, said that he is not optimistic about a change in U.S. behavior toward Iran, but that he is confident that the talks will yield positive results.

“As the supreme leader announced, we support the nuclear talks,” Larijani said. “The framework of the talks is meant to maintain the dignity of our country.”

Booth reported from Jerusalem. Karen DeYoung in Tel Aviv, Israel and Amman, Jordan; and Jason Rezaian in Washington contributed to this report.