Iran and six world powers meeting in Geneva have reached a deal on Tehran’s nuclear programme, foreign ministers say.
No details have been released about the agreement, which has been reached after five days of negotiations.
Negotiators from the UK, US, Russia, China, France and Germany want Iran to stop enriching uranium in return for a loosening of sanctions.
Iran had earlier said it insisted on a “right to enrichment” in any deal.
This deal may be the most significant agreement between the world powers and Iran for a decade, says the BBC’s Iran correspondent, James Reynolds, who is at the talks in Geneva.
Iranian and western negotiators are expected to speak at a news conference shortly.
US President Barack Obama will give a statement at 03:15 GMT.
Iran’s nuclear sites
Tehran denies repeated claims by Western governments that it is seeking to develop nuclear weapons, and insists it must be allowed to enrich uranium for power stations.
“We have reached an agreement,” the Iranian Foreign Minister Mohammad Javad Zarif announced on his Twitter feed.
French Foreign Minister Laurent Fabius also confirmed the deal.
Minutes earlier, Michael Mann, spokesman for the EU foreign policy chief Baroness Catherine Ashton, who is leading the conference, quoted her as saying: “We have reached agreement between E3+3 and Iran.”
No details have been released. The White House says the US president, Barack Obama – who is in Washington – is preparing to make a statement about the deal.
Earlier, on Saturday evening, the deputy Iranian foreign minister, Abbas Araqchi, said “98% of the draft” had been agreed but that Tehran wanted a “right to enrichment” to be clearly stated in any deal.
“We are insisting on our right to enrichment, which should be clearly recognised in the draft agreement,” Mr Araqchi was quoted as telling Iranian reporters late on Saturday – the fourth day of the negotiations.
Negotiators have been working since Wednesday to reach an agreement that is acceptable to both sides.
The talks had been scheduled to finish on Friday but were extended. Foreign ministers from the so-called P5+1 group of nations joined on Saturday, amid hopes of a breakthrough.
US officials said Secretary of State John Kerry, who arrived in Geneva early on Saturday, had the goal of “continuing to help narrow the differences and move closer to an agreement”.
British Foreign Secretary William Hague said on Saturday that a deal would be done only if it was a “truly worthwhile agreement”.
Some US politicians had said they would push for more sanctions if the talks failed.
The Geneva meeting follows a previous round of talks earlier this month.
On that occasion, foreign ministers flew to Geneva to conclude the negotiations, but they went home empty-handed.
Analysts say a major sticking point has been Iran’s insistence on its right to enrich uranium – a process that yields material used to manufacture fuel for power stations, but can also be used in weapons.
Western diplomats are also concerned about a reactor Iran is building at Arak – an issue which disrupted the first round of talks.
President Obama has said any interim agreement would see the bulk of international and US sanctions remain, but that Iran would get sanctions relief worth between $6bn and $7bn.
The essence of the deal would involve Iran making no more advances in its nuclear programme and agreeing to “more vigorous inspections”, he said.