GENEVA — Negotiations in Geneva over Iran’s nuclear program have “reached the final moment,” Chinese Foreign Ministry spokesman Hong Lei said Saturday.

Lei’s comment, communicated by Xinhua, came as Chinese Foreign Minister Wang Yi left Beijing to attend the talks.

Earlier Saturday, German Foreign Minister Guido Westerwelle announced he would also fly to Geneva to attend the negotiations, on the heels of a US State Department announcement that US Secretary of State John Kerry would attend the talks.

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Kerry’s wish to attend raised expectations that a deal to curb Tehran’s nuclear program could be in the works.

British Foreign Secretary William Hague announced late Friday that he was also flying to Geneva, and French diplomatic sources said Foreign Minister Laurent Fabius would join them.

Before departing for Geneva, Kerry told reporters he was optimistic that a deal with Iran could be struck — but not necessarily over the next two days. Kerry anticipated flying on to Israel if it an agreement is signed to immediately brief Prime Minister Benjamin Netanyahu on the terms.

Netanyahu has been publicly castigating the US over the terms of the emerging deal — which provides for a partial freeze in the Iranian program and the easing of some sanctions — and imploring Kerry not to sign it. Netanyahu has also vowed to “stand alone” if necessary to prevent Iran attaining nuclear weapons.

In Canada on Friday, Israel’s Defense Minister Moshe Ya’alon echoed Netanyahu’s description of the likely deal as “bad.” Ya’alon, who held talks with his US counterpart Chuck Hagel, acknowledged the differences between the US and Israel over the deal, but also stressed the fundamental closeness of the US-Israel alliance.

State Department spokeswoman Jen Psaki said Kerry would arrive in Geneva early Saturday, joining Russian Foreign Minister Sergey Lavrov, who arrived Friday. The arrival of the foreign ministers will lend weight to negotiations aimed at beginning a rollback of Iran’s nuclear program in exchange for easing US and international sanctions.

In a short statement, Psaki confirmed that “after consulting with EU High Representative Ashton and the negotiating team on the ground, Secretary Kerry will travel to Geneva later today with the goal of continuing to help narrow the differences and move closer to an agreement.”

Just two hours earlier, when asked whether Kerry would travel to Switzerland, Psaki would not confirm any such plans. But the secretary’s schedule had been kept open for Friday since the beginning of the week, a fact that had contributed to speculation that he intended to visit Israel.

Negotiators have been working since Wednesday to find language acceptable to Iran and its six negotiating partners — the US, Russia, China, France, Britain and Germany.

As negotiations moved into the evening Friday, a diplomat in Geneva for the talks said some progress was being made on a key sticking point — Iran’s claim to a right to produce nuclear fuel. Iranian Foreign Minister Mohammad Javad Zarif and Catherine Ashton, the European Union’s top diplomat, have met repeatedly since Wednesday trying to resolve that and other differences.

Israel’s Channel 2 said Iranian participants in the talks claim the P5+1 countries had recognized Iran’s “right” to enrich uranium — a key concession bitterly opposed by Israel as legitimizing Iran’s nuclear program.

The last round of talks between Iran and the six world powers ended Nov. 10 with no deal even after Kerry, Lavrov, the foreign ministers of Britain, France and Germany and a Chinese deputy foreign minister flew in and attempted to bridge differences.

Zarif and Ashton met briefly Friday for talks that Iran’s official IRNA news agency described as “complicated and tough.” It quoted Iranian Deputy Foreign Minister Abbas Araqchi in Geneva as saying that Iran’s right to uranium enrichment must be part of any deal.

Iran says it is enriching only for reactor fuel, medical uses and research. But the technology can also produce nuclear warhead material.

Zarif last weekend indicated that Iran is ready to sign a deal that does not expressly state Iran’s right to enrich, raising hopes that a deal could be sealed at the current Geneva round.

On Wednesday, however, Iran’s supreme leader, Ayatollah Ali Khamenei, said his country would never compromise on “red lines.” Since then Tehran has reverted to its original line — that the six powers must recognize this activity as Iran’s right under the nuclear Nonproliferation Treaty despite strong opposition by Israel and within the US Congress.

A senior Iranian negotiator said that the Iranian claim did not need to be explicitly recognized in any initial deal, despite Khamenei’s comment. He did suggest, however, that language on that point remained contentious, along with other differences.

The diplomat said work was proceeding on a compromise along the lines of what the Iranian negotiator said — avoiding a direct reference to any country’s right to enrich but still giving enough leeway for Iran to accept it.

Both he and the Iranian envoy demanded anonymity because they were not allowed to discuss the closed negotiations.

Sanctions relief was also an issue.

The United States and its allies have signaled they are ready to ease some sanctions in return for a first-step deal that starts to put limits on Iran’s nuclear program. But they insist that the most severe penalties — on Tehran’s oil exports and banking sector — will remain until the two sides reach a comprehensive agreement to minimize Iran’s nuclear arms-making capacity.

Iran says it does not want such weapons and has indicated it’s ready to start rolling back its program but wants greater and faster sanctions relief than that being offered.

Several US senators — both Democrat and Republican — have voiced displeasure with the parameters of the potential agreement, arguing that the US and its partners are offering too much for something short of a full freeze on uranium enrichment.

Senate Majority Leader Harry Reid said Thursday that he would support legislation to expand sanctions against Iran, though he said he also backs the negotiating effort. Reid said the threat of more sanctions was essential to get an acceptable deal.

Sen. Bob Corker, the Republicans’ top member on the Senate Foreign Relations Committee, on Thursday proposed a bill outlining a final agreement, including an end to all Iranian enrichment activity, and seeking to restrict President Barack Obama’s capacity to ease sanctions.