Lausanne (AFP) - Russia and Iran's foreign ministers claimed a breakthrough early Wednesday in talks on a framework deal curtailing Tehran's nuclear programme, but the US said not all issues had been agreed yet, as discussions were suspended for the night.
"One can say with relative certainty that we at the minister level have reached an agreement in principle on all key aspects of the final settlement of this issue," Russian media quoted Sergei Lavrov as saying at talks in Switzerland.
This came after Russia's top diplomat and the foreign ministers of five other major powers and Iran continued working through the night as they missed a midnight (2200 GMT) deadline to agree the main outlines of what they hope will be an historic accord.
The powers hope a full agreement, due to be finalised by June 30, will see Iran scale back its nuclear capability to prevent Tehran developing nuclear weapons under the guise of its civilian programme.
The stakes are high, with fears that failure to reach a deal may set the United States and Israel on a road to military action to thwart Iran's nuclear drive, which Tehran says is purely peaceful.
With talks set to resume Wednesday morning, confusion remained about the exact status of the negotiations.
The "agreement in principle... will be put on paper in the coming hours or perhaps within one day," Lavrov said, quoted by Ria Novosti after a lengthy day of talks in Lausanne.
Iranian Foreign Minister Mohammad Javad Zarif said he hoped to complete later on Wednesday the outlines of the framework.
"We have accomplished quite a bit, but people needed to get some rest and start over early in the morning. I hope that we can finalise the work on Wednesday," Zarif told reporters.
A senior US official however said there was not yet full agreement on key points.
"All issues have not been agreed," a senior US official told AFP.
US Secretary of State John Kerry briefed President Barack Obama, and his national security team on the day's negotiations by secure video conference.
Obama "received an update on the current status of the negotiations," national security council spokeswoman Bernadette Meehan said, adding he had "thanked the team for their continuing efforts."
A Western diplomat also said there was no framework agreement yet.
French Foreign Minister Laurent Fabius meanwhile followed his Chinese counterpart Wang Yi in leaving Lausanne, with Fabius's office saying he would return "as soon as it is useful".
- Low on detail? -
Under the final accord, the powers want Iran to scale back its nuclear programme to give the world ample notice of any dash to make the bomb.
In return, the Islamic republic is demanding the lifting of crippling sanctions.
But the question is how much detail will be in the framework that Iran and the six powers -- the US, China, Russia, Britain, France and Germany -- want to nail down.
If it falls short of firm commitments by Iran, Obama will find it hard to fend off attempts by his Republican opponents to pass fresh sanctions on Tehran.
Iran's negotiators are also under pressure from domestic hardliners not to give too much away and for President Hassan Rouhani to deliver on his promises to win the lifting of sanctions.
Fresh US sanctions could torpedo the whole negotiating process launched after Rouhani became president in 2013.
Republicans fear that since some of its nuclear infrastructure will likely stay intact, Iran will still be able to get the bomb -- a concern shared by Israeli Prime Minister Benjamin Netanyahu.
"The greatest threat to our security and our future was and remains Iran's attempt to be armed with nuclear weapons. The agreement being formulated in Lausanne paves the way to that goal," Netanyahu said.
Saudi Arabia, which has led an Arab coalition bombing Iran-backed rebels in Yemen in recent days, is also alarmed by Tehran's rapprochement with the West.
Other areas of the mooted deal, including the future size of Iran's uranium enrichment capacity also appear to have been tentatively sewn up.
But the two sides still appear to be discussing other areas, including what to do with Iran's stockpiles of nuclear material, and how long the deal should last.