Talks seeking Iran nuclear deal to enter third day
Talks in Geneva on Iran's nuclear programme are to resume on Saturday, after Friday's discussions ended late in the evening.
Earlier US Secretary of State John Kerry said there were still "important gaps" between Iran and world powers.
Meanwhile, President Obama telephoned Israeli Prime Minister Benjamin Netanyahu to allay fears over any deal.
Under a deal being floated, Iran could freeze expansion of its nuclear activity for limited sanctions relief.
"It was productive but still we have lots of work to do," Iranian Deputy Foreign Minister Abbas Araqchi told reporters late on Friday.
For his part, Mr Kerry commented "we're working hard," as he returned to his hotel at the end of the evening.
A White House statement said Mr Obama had updated the Israeli leader on the talks in Geneva, and repeated his commitment to stopping Tehran getting a nuclear weapon.
Israeli Prime Minister Benjamin Netanyahu had earlier said he "utterly rejected" such a deal with Iran, its long-time enemy, and that his country would not be obliged to abide by it.
The West has suspected Iran's uranium enrichment programme is a step towards building nuclear weapons - a charge Iran strongly denies.
The talks of Friday ended after Iranian Foreign Minister Mohammad Javad Zarif held a five-hour meeting with top EU diplomat Catherine Ashton and Mr Kerry.
UK, French and German foreign ministers also joined the unscheduled talks with Iranian representatives in Geneva.
Russia's Sergei Lavrov had not been scheduled to attend but sources say he will travel to Geneva on Saturday.
For the first time in years, talks about Iran's nuclear programme are moving fast, the BBC's James Reynolds reports from Geneva.
The negotiations have also picked up new, critical purpose, he says - a chance for the US and Iran to explore an end to their three decades of mistrust.
However, although the sides appear closer to a breakthrough than during previous talks, the outcome still remains uncertain.
Mr Kerry interrupted the itinerary of his tour to the Middle East and North Africa to fly to Geneva after meeting Mr Netanyahu in Jerusalem.
The US state department also said that Mr Kerry would not now make planned stops in Algeria or Morocco.
On arrival, Mr Kerry said: "[We] hope to try to narrow the differences but no-one should mistake that there are important gaps to be closed."
The Geneva talks involve the P5+1: the US, Russia, the UK, France and China as permanent UN Security Council members, plus Germany.
The French, German and UK Foreign Ministers - Laurent Fabius, Guido Westerwelle and William Hague - are also in Geneva.
Mr Fabius said there had been progress but nothing "hard and fast".
Russian Deputy Foreign Minister Sergei Ryabkov said Moscow hoped the talks would produce a "lasting result the entire world has been waiting for".
Friday prayer leaders across Iran urged the public to support the country's nuclear delegation as it negotiated "from a position of strength and with dignity".
Mr Zarif said on Friday there was "the general outline of an agreement".
Although details of the suggested deal have not been disclosed, it is thought to offer Iran a gradual easing of sanctions in return for a freeze on expansion of nuclear activities.
The Israeli prime minister argued the Iranians were getting sanctions relief while "not reducing in any way their nuclear enrichment capability".
Israel, Mr Netanyahu said, would do "everything it needs to do to defend itself and the security of its people".
He has said Israel is committed to making sure Tehran never gets a nuclear weapon. Defence analysts have speculated the Israelis may take military action to disrupt Iran's programme.
White House spokesman Josh Earnest said that any criticism of a deal was "premature".
"There is no deal, but there is an opportunity here for a possible diplomatic solution, and that is exactly what [President Obama] is pursuing," he said.
Since 2006 the UN Security Council has imposed a series of sanctions - including asset freezes and travel bans - on entities and people involved in Iran's nuclear programme.
Separate US and EU sanctions have targeted Iran's energy and banking sectors, crippling its oil-based economy.
The head of the UN atomic watchdog, the International Atomic Energy Agency, Yukiya Amano, is travelling to Tehran on Monday to meet senior Iranian figures.