U.S. Secretary of State John Kerry arrived in Geneva on Saturday to join talks on Iran's contested nuclear program, as Tehran and six world powers appeared to be on the verge of a breakthrough in the decade-old dispute.
The Chinese, French, British and German foreign ministers - Wang Yi, Laurent Fabius, William Hague and Guido Westerwelle - were due along with Kerry to take part in intense negotiations on a deal under which Iran would curb its atomic activity in exchange for some relief from economic sanctions.
The announcements came after diplomats in the Swiss city said a major sticking point in the talks, which began on Wednesday, may have been overcome.
A senior European diplomat told reporters earlier that foreign ministers of the six states would come to Geneva only if there was a deal to sign. "We have made progress, including core issues," the diplomat said.
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France's Foreign Minister, who spoke out against a draft deal floated at the November 7-9 negotiating round, appeared guarded on arrival in Geneva early on Saturday.
"I hope we can reach a deal, but a solid deal. I am here to work on that," he said.
France has consistently taken a tough line over Iran's nuclear program, helping Paris forge closer ties with Tehran's foes in Israel and the Gulf.
However, a French diplomatic source urged caution.
It's the home stretch, but previous negotiations have taught us to be prudent."
Russian Foreign Minister Sergei Lavrov arrived in Geneva on Friday evening and met Iranian Foreign Minister Mohammad Javad Zarif and EU foreign policy chief Catherine Ashton, a Russian spokeswoman said.
Kerry left for Geneva "with the goal of continuing to help narrow the differences and move closer to an agreement," State Department spokeswoman Jen Psaki said.
The decision was taken after consulting with Ashton, who is coordinating talks with Iran on behalf of the United States, Russia, China, France, Britain and Germany, Psaki said.
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Later, deputy State Department spokeswoman Marie Harf said that Kerry decided to travel to Geneva "in light of the progress being made" and with "the hope that an agreement will be reached".
Echoing optimism that a deal was close, China's state-run Xinhua news agency quoted a foreign ministry spokesman as saying the talks "have reached the final moment". The country's foreign minister left Beijing for Geneva early on Saturday.
Diplomats said a compromise over Iran's insistence that its "right" to enrich uranium be internationally recognised has been proposed, possibly opening the way to a long-sought breakthrough.
The United States and other Western powers say there is no such thing as a right to enrich - a process that can yield both electricity and nuclear bombs - but Iran views it as a matter of national sovereignty and crucial to any deal that would resolve the standoff over its nuclear intentions.
The Islamic Republic also wants relief from economic sanctions in return for any nuclear concessions it makes that could allay the West's suspicions that its nuclear fuel-making program has military rather than its stated civilian goals.
Foreign ministers from the six nations negotiating with Iran waded into the previous talks on Nov. 7-9 and came close to winning concessions from Iran, which they count on to reduce the risk of Iran achieving a nuclear weapons capability.
Politically charged details
In the days running up to the talks, policymakers from the six powers said an interim accord on confidence-building steps could be within reach to start a cautious process of detente with Iran and banish the spectre of a wider Middle East war.