"Implementation Day" for the accord came after the International Atomic Energy Agency said its "inspectors on the ground verified that Iran has carried out all measures" agreed under the agreement. EU foreign policy chief Federica Mogherini, representing the six world powers, said that as a result "multilateral and national economic and financial sanctions related to Iran's nuclear programme are lifted".

These will include sanctions on Iran's lifeblood oil exports and open up the 80-million-strong country to business. Rouhani has predicted a "year of prosperity" for his country. "This achievement clearly demonstrates that with political will, perseverance, and through multilateral diplomacy, we can solve the most difficult issues," Mogherini said in Vienna in a joint statement with Iranian Foreign Minister Mohammad Javad Zarif.

The announcement also followed news of a prisoner swap between Iran and the United States in another sign of thawing relations between the two foes since the agreement was struck. The steps taken by Iran, combined with ultra-close IAEA inspections, extend to at least a year - from a few months previously - how long Iran would need to make one nuclear bomb's worth of fissile material.

They include slashing by two-thirds its uranium centrifuges, reducing its stockpile of uranium - enough before the deal for several bombs - and removing the core of the Arak reactor which could have given Iran weapons-grade plutonium. Iran has always denied wanting nuclear weapons, saying its activities are exclusively for peaceful purposes such as power generation.

"Today... the United States, our friends and allies in the Middle East, and the entire world are safer because the threat of the nuclear weapon has been reduced," US Secretary of State John Kerry said in Vienna.

UN Secretary-General Ban Ki-moon said it was a "significant milestone that reflects the good faith effort by all parties to fulfil their agreed commitments." British Foreign Secretary Philip Hammond, one of the six powers with the US, Russia, China, France and Germany, said that "years of patient and persistent diplomacy... have borne fruit".

German Foreign Minister Frank-Walter Steinmeier called the implementation of the nuclear deal "a historic success for diplomacy". In what was hailed last July as a momentous diplomatic breakthrough, the Vienna agreement was nailed down after two years of rollercoaster negotiations following the moderate Rouhani's June 2013 election.

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