GENEVA — Iranian Deputy Foreign Minister Abbas Araghchi expressed doubt that a deal between world powers and Tehran over its controversial nuclear program could be reached Saturday, on the fourth consecutive day of talks.

“Intense and difficult negotiations are under way and it is not clear whether we [will] reach an agreement tonight,” Fars news agency quoted Araghchi as saying, as translated by AFP. “The dispute is over the wording,” he added, without indicating whether talks would continue for a fifth day.

“We have now entered a very difficult stage,” Iranian Iranian Foreign Minister Mohammad Javad Zarif was quoted by AFP Saturday as telling Iranian state media.

The State Department, meanwhile, announced Saturday that US Secretary of State John Kerry would travel to London on Sunday to meet with Britain’s Foreign Secretary William Hague and the Libyan prime minister, a move which may indicate that, with or without a deal, negotiations with Iran will end Saturday night — at least for this round.

Kerry met with top European Union diplomat Catherine Ashton and Zarif for nearly two hours earlier Saturday to discuss the details of the emerging deal, but no statements were issued.

The US secretary of state and the world’s other top diplomats joined Iran nuclear talks Saturday, cautioning there were no guarantees their participation would be enough to seal a deal to curb Tehran’s rogue program in return for limited sanctions relief.

The goal is a six-month agreement to partially freeze Iran’s nuclear program while offering Iran incentives through limited sanctions relief. If the interim deal holds, the parties would negotiate final stage deals to ensure Iran does not build nuclear weapons.

But it was unclear whether the current round, which began Wednesday, would produce any first-stage deal.

British Foreign Secretary William Hague speaks to journalists as he arrives at the Intercontinental Hotel prior to talks on Iran's nuclear program in Geneva, Switzerland, Saturday, Nov. 23, 2013. (photo credit: AP Photo/Keystone,Jean-Christophe Bott)

British Foreign Secretary William Hague speaks to journalists as he arrives at the Intercontinental Hotel prior to talks on Iran’s nuclear program in Geneva, Switzerland, Saturday, Nov. 23, 2013. (photo credit: AP Photo/Keystone,Jean-Christophe Bott)

Hague spoke of “very difficult negotiations,” saying “narrow gaps” remain on the same issues that blocked agreement at the last round earlier this month.

“We’re not here because things are necessarily finished,” Hague told reporters. “We’re here because they’re difficult, and they remain difficult.”

Kerry and his counterparts from Russia, Britain, France, China and Germany headed for Geneva after diplomats said Friday that Zarif and Ashton had made progress on a key sticking point — Iran’s claim to a right to produce nuclear fuel through uranium enrichment.

Details were not released but it appeared the two sides were trying to reconcile Iran’s insistence that it has a right to enrich for peaceful purposes while assuaging fears that Tehran was secretly trying to build a bomb, a charge the Iranians deny.

US Secretary of State John Kerry, left, and French Foreign Minister Laurent Fabius sit together during a photo opportunity before a meeting, Saturday, Nov. 23, 2013, in Geneva, Switzerland. (photo credit: AP Photo/Carolyn Kaster, Pool)

US Secretary of State John Kerry, left, and French Foreign Minister Laurent Fabius sit together during a photo opportunity before a meeting, Saturday, Nov. 23, 2013, in Geneva, Switzerland. (photo credit: AP Photo/Carolyn Kaster, Pool)

As the talks entered an intensive phase, Chinese Foreign Ministry spokesman Hong Lei said the negotiations had reached “the final moment,” according to China’s Xinhua news agency.

Zarif warned Saturday afternoon that the Islamic Republic would not give in to “excessive demands” of the world powers as the nuclear talks entered what he called a “critical phase.”

Araghchi said earlier Saturday morning that there were only “two or three more points of disagreement” between the Islamic Republic and the P5+1 powers over the tentative deal. “The two sides are close to an agreement,” he said. “We must see if we can resolve these differences.”

Unnamed Arab officials also told CNN that a deal with Iran seemed “very near.”

Others were less upbeat.

Germany’s Foreign Minister Guido Westerwelle spoke of “a realistic chance” for a deal but said “there is still a lot of work to do.” Russian Deputy Foreign Minister Sergei Ryabkov told RIA-Novosti news agency that negotiations were very close to a breakthrough but “unfortunately I cannot say that there is assurance of achieving this breakthrough.”

French Foreign Minister Laurent Fabius told reporters he wanted “a deal — but a solid deal — and I am here to work toward that end.”

Fabius’s brief comments conveyed a guarded tone compared to his public comments during the previous round of talks two weeks earlier that fanned talk of disunity among the world powers negotiating with Iran.

France’s concern that the negotiators were rushing into a flawed deal with Iran helped delay an agreement during a session nearly two weeks ago.

Other obstacles include Iran’s plutonium reactor under construction in Arak as well as a formula for providing limited sanctions relief without weakening international leverage against Iran.

The arrival of the foreign ministers followed a day in which diplomats appeared more and more optimistic that a deal could be struck.

Before departing for Geneva Friday, Kerry told reporters he was optimistic that a deal with Iran could be struck — but not over the next two days. Kerry reportedly 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 has implored 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.

As talks in Geneva adjourned for the day on Friday night, a diplomat said Zarif and Ashton had made progress on the issue of Iran’s claim to a right to uranium enrichment. Iran’s official IRNA news agency quoted Araghchi in Geneva as saying that Iran’s right to uranium enrichment must be part of any deal, and Zarif told Iran’s Press TV that Iran’s “right” to peaceful nuclear energy, “including enrichment,” must be respected.

Israel’s Channel 2 said Friday night that Iranian participants in the talks claimed 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.

US Secretary of State John Kerry arrives at Geneva International airport, Saturday, Nov. 23, 2013, in Geneva, Switzerland, for the Iran nuclear talks. (photo credit: AP Photo/Carolyn Kaster, Pool)

US Secretary of State John Kerry arrives at Geneva International airport, Saturday, Nov. 23, 2013, in Geneva, Switzerland, for the Iran nuclear talks. (photo credit: AP Photo/Carolyn Kaster, Pool)

Enrichment is a hot-button issue because it can be used both to make reactor fuel and to arm nuclear missiles. Iran argues it is enriching only for power, and scientific and medical purposes. And it says it has no interest in nuclear arms.

But Washington and its allies point to Tehran’s earlier efforts to hide enrichment and allege it worked on developing such weapons.

Iran has insisted on that right throughout almost a decade of mostly fruitless nuclear negotiations. But Zarif last weekend indicated that Iran is ready to sign a deal that does not expressly state that claim, raising hopes that a deal could be sealed at the current Geneva round.

For the US and Iran, the talks represent more than trying to hammer out a nuclear deal. In style and substance they are an extension of the historic dialogue opened during September’s annual U.N. gathering, which included a 15-minute phone conversation between President Barack Obama and Iran’s new president, Hassan Rouhani.

The nuclear negotiations have included intensive one-on-one sessions between US and Iranian envoys, offering opportunities to widen contacts and begin the long process of reconciliation after more than three decades of estrangement. For Iran, it also gives Rouhani’s government a chance to show skeptical hard-liners that dialogue is possible with Washington without putting the country’s Islamic system in peril.

Iranian hard-liners are suspicious of talk of nuclear compromise since Rouhani took office in September, fearing his team will give too much at the negotiating table and not get enough in terms of sanctions relief.

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

EU foreign policy chief Catherine Ashton, center, next to members of her delegation attends talks over Iran's nuclear program in Geneva on Friday Nov. 22, 2013. (photo credit: AP PhotoFabrice Coffrini,Pool)

EU foreign policy chief Catherine Ashton, center, next to members of her delegation attends talks over Iran’s nuclear program in Geneva on Friday Nov. 22, 2013. (photo credit: AP PhotoFabrice Coffrini,Pool)

Still, comments from Iranian officials in Geneva indicated that reverting to tough talk on enrichment may be at least partially meant for home consumption.

In Geneva, a senior Iranian negotiator said the Iranian claim to the right to enrich did not need to be explicitly recognized in any initial deal, despite Khamenei’s comment, adding that the supreme leader was not planning to intervene in the talks. He did suggest, however, that language on that point remained difficult and that there were other differences.

Work is 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, said a diplomat involved in the talks.

Senior Iranian analyst Trita Parsi, citing conversations with Iranian and US officials, said the draft includes a reference to the nuclear Non-Proliferation Treaty, which Iran claims is the guarantor of each country’s right to enrich by granting signatories the right to pursue nuclear power for peaceful uses.

That argument is rejected by the United States and its allies, which say the treaty does not directly mention such a right.

Parsi said Tehran wants the wording to make clear that Iran is not a “permanent outcast,” but has the same rights and responsibilities as all other signatories to the treaty.

Russia and China in recent years have signaled acceptance of Iran’s demand that its right to enrich for peaceful purposes be recognized, and Germany supports the right of any country to that activity as long as it is peaceful. But the other three nations at the table with Iran — the United States, Britain and France — have continued to balk.

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.

The United States and its negotiating partners 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.

EU foreign policy chief Catherine Ashton, second left, and Iranian Foreign Minister Mohammad Javad Zarif, third right, are pictured during talks over Iran's nuclear program in Geneva, Switzerland, on Friday. (photo credit: AP/Fabrice Coffrini)

EU foreign policy chief Catherine Ashton, second left, and Iranian Foreign Minister Mohammad Javad Zarif, third right, are pictured during talks over Iran’s nuclear program in Geneva, Switzerland, on Friday. (photo credit: AP/Fabrice Coffrini)

They want Iran to stop enriching to a level higher than its main stockpile and only a technical step away from weapons-grade uranium as part of such a deal. They also seek limits on overall enrichment, and a formulation that reduces the proliferation danger from a reactor Iran is building that will produce enough plutonium for up to two weapons once completed.

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.

No details on relief offered have been made public. And the US administration has not commented on reports from congressional officials that Obama’s team estimates Iran could get $6 billion to $10 billion in benefits over six months for rolling back its nuclear program.

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.

In Moscow this week to meet with Russian President Vladimir Putin, Netanyahu renewed his demand for a halt to all Iranian nuclear programs that could be turned from peaceful uses to making weapons.

Israel wants a settlement that is “genuine and real,” he said.

“Israel believes that the international community must unequivocally ensure the fulfillment of the UN Security Council’s decisions so that uranium enrichment ends, centrifuges are dismantled, enriched material is taken out of Iran and the reactor in Arak is dismantled,” continued Netanyahu, referring to Iran’s plutonium reactor under construction.

“They must not have nuclear weapons,” he told a gathering of Russian Jews. “And I promise you that they will not have nuclear weapons.”