US Secretary of State John Kerry will fly to Geneva to join talks on Iran's nuclear program Friday, a sign that the negotiations might have made progress.
A State Department spokeswoman said Kerry's decision came after talking to the European Union's foreign policy chief Catherine Ashton. She added that Kerry's main goal was "help narrow the differences and move closer to an agreement."
Earlier in the day, Russian Foreign Minister Sergei Lavrov arrived in Geneva to join the talks between Iran and the so-called P5+1 — the United States, China, France, Britain and Germany.
On Friday night, both French Foreign Minister Laurent Fabius and British Foreign Secretary William Hague confirmed that they will also be attending the negotiations.
The Chinese foreign minister is also expected to arrive Saturday.
Iran and the six powers struggled to overcome stumbling blocks to an interim deal under which Tehran would curb its contested nuclear program in exchange for some relief from economic sanctions.
Iranian Foreign Minister Mohammad Javad Zarif, Tehran's chief negotiator, said significant headway had been made.
"We are negotiating our differences and we have made considerable progress," he said. "In some cases we have had results ... but still we have three, four differences."
The six foreign ministers joined intense talks on November 7-9 and came close to winning concessions from Iran they count on to reduce the risk of an Iranian nuclear weapon.
According to a draft proposal hammered out on November 9, the P5+1 wanted Iran to freeze for six months key parts of its nuclear program.
In return Iran would get minor and, Western officials insist, "reversible" sanctions relief, including unlocking several billion dollars in oil revenues and easing trade restrictions on precious metals and aircraft parts.
Optimism seems to have waned since then as the sides have since Wednesday bogged down in politically vexed details, hampered by stubborn mutual mistrust that has characterized a decade-old standoff with Iran over its nuclear intentions.
This third meeting since President Hassan Rouhani's election in June is seen as the biggest hope in years to resolve the decade-old standoff over Iran's nuclear programme.
Failure might mean Iran resuming the expansion of its atomic activities, Washington and others adding to already painful sanctions, and possible Israeli military action.
At the last gathering two weeks ago foreign ministers including US Secretary of State John Kerry flew to Geneva but three days of intense talks failed and they went home empty-handed.
Reuters and Agence France-Presse contributed to this report.