German Foreign Minister Guido Westerwelle
will join US Secretary of State John Kerry and other world power counterparts on Saturday for nuclear talks with Iran
, a spokesman said.
"The foreign minister will be in Geneva on Saturday," a spokesman told AFP.
Russian Foreign Minister Sergei Lavrov is already in Geneva and is due to be joined on Saturday by Kerry, Britain's William Hague and France's Laurent Fabius.
It is be the second time in two weeks that Kerry and other top diplomats will hunker down in a smart Geneva hotel after intensive talks that ultimately failed shortly after midnight there on November 10th.
Kerry decided to go back for another try "in light of the progress being made" and "with the hope that an agreement will be reached", State Department spokesperson Marie Harf said Friday.
The announcements of the foreign minister arrivals came as a third day of discussions between Iran
and political directors from the United States, Russia, China, Britain, France and Germany -- the P5+1 -- continued until around 12.30.
This third round of talks 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, which world powers want halted but which Tehran insists is peaceful.
Failure might mean Iran resuming the expansion of its atomic activities, Washington and others adding to already painful sanctions, and possible Israeli and even US military action.
Both sides say they want a deal but getting an accord palatable to hardliners in the United States and in the Islamic republic -- as well as Israel -- is tough.
According to a draft proposal, the United States, Britain, China, France, Russia, and Germany -- the P5+1 -- want Iran to freeze for six months key parts of its nuclear programme.
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.
This hoped-for "first phase" deal would build trust and ease tensions while negotiators push on for a final accord that ends once and for all fears that Tehran will get an atomic bomb.
Friday's third day of talks in Geneva saw a narrowing of differences as Iranian Foreign Minister Mohammad Jarad Zarif met with P5+1 chief negotiator and EU foreign policy chief Catherine Ashton.
"To a good degree, we have moved (closer) towards agreement," deputy foreign minister Abbas Araqchi told Iranian media late Friday, adding however that "some main issues still remain."
"God willing we will reach a result," Zarif told Iranian media, saying there was "room for optimism".
Lavrov held a meeting late Friday with Zarif and later with Ashton.
Reports said two issues remained real sticking points: Iran's "right" to uranium enrichment and its Arak reactor, which could provide Iran with weapons-grade plutonium.
Mark Hibbs, analyst at the Carnegie Endowment for International Peace, said the fact that Kerry was coming to Geneva again showed a deal was near.
"If it isn't very close, I can't believe that Kerry would expend the political capital to cross the pond for this, especially with Congress breathing down his neck," Hibbs told AFP.
Many in Israel, widely assumed to have a formidable nuclear arsenal itself, are alarmed about the mooted deal, with Prime Minister Benjamin Netanyahu campaigning vigorously against it.
Netanyahu wants all of Iran's nuclear infrastructure dismantled, not parts of it frozen, believing that the P5+1 will leave Iran with an ability to develop nuclear weapons.
In the United States meanwhile there is a push by lawmakers to ignore President Barack Obama's pleas and pass yet more sanctions on Iran if there is no deal -- or one seen as too soft.
This risks spoiling Iran's apparent newfound appetite for rapprochement with the West since the cleric Rouhani, himself a former nuclear negotiator and seen as a relative moderate, replaced the more hardline Mahmoud Ahmadinejad in August.
Rouhani is under pressure to show the supreme leader Ayatollah Ali Khamenei the first fruits of his "charm offensive", and it is unclear whether the minor sanctions relief on offer is enough.