And deputy foreign minister Abbas Araqchi said on Twitter Iran’s “enrichment programme has been recognised”, but did not elaborate whether it was mentioned in the agreement.

Iran had been pushing for what it calls its “right” to enrich uranium to be recognised by the United States, Britain, France, China and Russia plus Germany.

The announcement came after more than four days of talks in Geneva between Iran and the five permanent members of the UN Security Council members plus Germany, chaired by Ashton, who is the European Union’s top diplomat.

The talks were aimed at getting Iran to scale back parts of its nuclear programme in return for relief from painful sanctions imposed by the UN Security Council and Western countries.

It was the third meeting in Geneva since Hassan Rouhani became Iranian president in August. The reputed moderate has raised hopes for an end to the decade-old stand-off over Iran’s nuclear work.

Numerous diplomatic initiatives have failed over the past 10 years to persuade Iran to rein in its programme, which Tehran insists is peaceful but which Western countries suspect is aimed at crafting atomic weapons.

Foreign ministers from the six powers including US Secretary of State John Kerry had jetted into Geneva for the second time in two weeks on Saturday morning after negotiators made good progress.

Hopes they would quickly sew up the agreement faded however as the talks dragged on throughout Saturday and until the early hours of Sunday morning and the announcement at 3am.

In particular they appeared to snag on Iran’s insistence to have its “right” to enrich uranium formally recognised by the six powers, something Western countries strictly opposed.

It was unclear how this tricky issue has been got around in the new deal. Officials were due to give press conferences later on Sunday.

The powers were aiming to get Iran to suspend Iran’s enrichment of uranium -- which has civilian but at high purities also military uses -- at medium levels, which is close to weapons grade.

They also wanted construction stopped at a new reactor at Arak which could provide Tehran with plutonium, an alternative to highly-enriched uranium for a nuclear weapon.

In return they were offering Iran minor and “reversible” relief from painful sanctions, including unlocking several billion dollars in oil revenues and easing some trade restrictions.

This “first phase” interim deal is meant to build trust and ease tensions while negotiators push on for a final accord to end once and for all fears that Tehran will acquire an atomic bomb.

It remains to be seen, however, whether the deal, once the details are known, will go down with hardliners in the United States and the Islamic republic, as well as in Israel.

Iranians are impatient to see a lifting as soon as possible of sanctions that have more than halved Iran’s vital oil exports since mid-last year.

Iran’s currency, the rial, has been depreciated by more than half since late 2011, while inflation has soared to more than 40 per cent, according to questionable official figures.

At the same time Iran’s nuclear programme is a source of great national pride and supreme leader Ayatollah Ali Khamenei is loath to give it up.

Many in Israel though strongly believe that the only aim of Iran -- an ally of Hezbollah and embattled Syrian President Bashar al-Assad -- is to develop a nuclear arsenal.

Many hardliners in the United States agree.

Israel, itself widely assumed to be the Middle East’s only nuclear-armed nation, has refused to rule out military action against its arch rival.

Israel's government on Sunday denounced the agreement as a “bad deal” and an "historic mistake" that Israel did not regard itself as bound by.

“Israel does not see itself as bound by this bad, this very bad agreement that has been signed,” Economic Minister Naftali Bennett, a member of Netanyahu’s security Cabinet, told Israel’s Army Radio.

Netanyahu, speaking to Israel's Cabinet, said: “Today the world became a much more dangerous place because the most dangerous regime in the world made a significant step in obtaining the most dangerous weapons in the world.”

President Obama planned to talk to Netanyahu on Sunday about Israel’s concerns, a senior US official said.

Russia’s Foreign Minister Sergei Lavrov praised the deal and said it would benefit all sides.

“Nobody lost, everyone ends up winning,” Russian news agencies quoted him as saying after marathon talks concluded in Geneva.

China on Sunday welcomed the breakthrough, saying the agreement with Tehran would “help safeguard peace and stability in the Middle East”.

“This agreement will help to uphold the international nuclear non-proliferation system, [and] safeguard peace and stability in the Middle East,” Foreign Minister Wang Yi said, according to a statement on the foreign ministry's website.