VIENNA (REUTERS/AFP) - Iran and six major powers have reached a historic nuclear deal, which will grant Teheran sanctions relief in exchange for curbs on its nuclear programme, an Iranian diplomat said on Tuesday.

Iran and six world powers, at a final meeting in Vienna on Tuesday, formally concluded a historic deal aimed at ensuring that Iran does not obtain the nuclear bomb, the EU's foreign policy chief Federica Mogherini announced Tuesday.

"Iran Talks done. We have the agreement," she said in a tweet, shortly after she chaired a final plenary session of foreign ministers from the so-called P5+1 and Iran ended in Vienna, ahead of an expected formal announcement of a deal which will see Teheran scale down its nuclear activities in exchange for relief from sanctions.

A United Nations Security Council resolution setting out timelines for Iran's compliance with a nuclear deal could be introduced as soon as next week, a senior US administration official said on Tuesday.

The US-drafted resolution will come "probably as soon as next week" and already has the backing of UN veto-wielding members who took part in the Iran talks, the official said.

"All the hard work has paid off and we sealed a deal. God bless our people," a diplomat told Reuters.

An Iranian negotiator also said the long-running haggling had reached a "successful conclusion".

The head of the UN atomic watchdog said he had signed a "roadmap" with Iran for probing suspected efforts to develop nuclear weapons, a key part of an overall accord.

International Atomic Energy Agency (IAEA) chief Yukiya Amano said he aimed to issue a report on the watchdog's investigation by Dec 15.

The landmark deal is expected to sharply curb Iran's nuclear programme and impose strict UN inspections in order to make any drive to make nuclear weapons all but impossible and easily detectable.

In return, the web of UN and Western sanctions choking Iranian oil exports and the economy of the country of 78 million people would be progressively lifted.

Iran has also accepted a so-called "snapback" plan that will restore sanctions in 65 days if it violates a deal agreed with six world powers to curb the country's nuclear programme, diplomats told Reuters on Tuesday.

The diplomats said a UN arms embargo would remain in place for five years, and UN missile sanctions would stay in place for eight years.

Teheran and the six powers had been holding marathon diplomatic negotiations at the ministerial level for more than two weeks to resolve a 12-year stand-off over Iran's nuclear programme.

The breakthrough came on the 18th day of marathon talks between Teheran and the so-called P5+1 - the United States, Russia, China, Britain, France and Germany in Vienna.

The diplomatic push began when Iranian President Hassan Rouhani came to power in 2013.

In November that year, an interim deal was agreed but two deadlines in 2014 for a lasting accord were missed.

Then in April, the parties scored a major breakthrough by agreeing the main outlines of an accord, aiming to finalise it by June 30, a deadline since pushed back twice.

Since April, legions of legal and technical experts have made great strides working out the nuts and bolts of how the highly ambitious and technical agreement will work.

The final hurdles had included the exact timing and pace of sanctions relief and Iran's desire to have a UN arms embargo lifted.

Foreign ministers including US Secretary of State John Kerry huddled late into the night at Vienna's Palais Coburg.

China's Foreign Minister Wang Yi told reporters as he arrived on Monday that there should be "no more delays", adding that no deal could be "perfect".

Also present were Russian Foreign Minister Sergei Lavrov and his counterparts from Britain, France and Germany - Philip Hammond, Laurent Fabius and Frank-Walter Steinmeier.

The agreement is a diplomatic victory for US President Barack Obama, who made the talks a centrepiece of his foreign policy, as well as for Mr Rouhani, a moderate seeking to bring his country in from the diplomatic wilderness.

They have faced opposition from hardliners from home, as well as from Iran's arch-foe Israel, believed to be the only country in the Middle East with atomic bombs, although it has never confirmed it.

Israeli Prime Minister Benjamin Netanyahu described the agreement as an historic mistake and said he woud do what he could to block Iran's nuclear ambitions.

"Iran is going to receive a sure path to nuclear weapons. Many of the restrictions that were supposed to prevent it from getting there will be lifted," Mr Netanyahu said at the start of a meeting with Dutch Foreign Minister Bert Koenders in Jerusalem.

"Iran will get a jackpot, a cash bonanza of hundreds of billions of dollars, which will enable it to continue to pursue its aggression and terror in the region and in the world. This is a bad mistake of historic proportions."

Earlier on Monday, Israeli Defence Minister Moshe Yaalon said: "We are heading toward a bad deal, and in the period after it we will of course have to continue preparing to protect ourselves on our own."

Saudi Arabia and other Sunni-ruled Gulf Arab states are also deeply suspicious of Shi'ite Iran, accusing it of fomenting unrest in Syria, Yemen and elsewhere in the Middle East.

Many in the United States, particularly among Mr Obama's Republican opponents, also say the mooted deal is too weak.

The agreement will prove a "hard sell" in the US Congress, which will have 60 days to chew over the accord, top Republican Mitch McConnell said in an interview broadcast on Sunday.