Iran has emerged from years of economic isolation after the UN nuclear watchdog ruled the Islamic Republic had curbed its nuclear programme under a deal with world powers, clearing the way for the lifting of crippling sanctions against Tehran.

In another sign of the easing of tensions between the West and Iran, Tehran and Washington announced an unexpected prisoner swap.

Iran will free five Americans including jailed Washington Post reporter Jason Rezaian and a Christian minister.

And in an unusual move, US President Barack Obama pardoned three Iranian-Americans charged for violating sanctions against Iran while prosecutors moved to drop charges against four Iranians outside the US.

Sanctions on Iran by the US, United Nations and European Union will be lifted within hours or days.

Mostly imposed in the last five years, the sanctions have cut off the country of 80 million people from the global financial system, reduced oil producer Iran's exports and imposed severe economic hardship on ordinary Iranians.

"Iran has carried out all measures required under the (July deal) to enable Implementation Day (of the deal) to occur," the Vienna-based International Atomic Energy Agency said in a statement.

The strengthening of Iran's economy could shift the geopolitical balance of the Middle East where Iran is the leading Shia Muslim power and its allies are fighting proxy wars in Iraq, Syria and Yemen against those who back its main Sunni Muslim regional rival, Saudi Arabia.

Iran's return to an already glutted oil market is one of the factors contributing to a global rout in oil prices, which fell below $30 a barrel this week for the first time in 12 years.

Tehran said it could boost exports by 500,000 barrels per day within weeks.