An academic says international sanctions lifted from Iran show the country wants a more constructive relationship with the rest of the world.

Sanctions against Iran have been lifted after the United Nations nuclear watchdog announced the country has satisfactorily scaled back its nuclear programme.

Otago University Professor of International Relations Robert Patman said it's an important deal because it opens up dialogue between the country and the rest of the world, and shows the country wants a more constructive relationship with the rest of the world.

"If we maintain a dialogue, this nuclear arms agreement, of which we are now seeing the fruits developing, could lead to a wider diplomatic dialogue on issues such as Syria."

He said it's striking that Russia, China, and the United States under the Obama administration were in one mind that it was very important to prevent Iran from developing a nuclear weapon.

Iran has the fourth largest oil reserves in the world, and they're about to hit global markets.

Patman said there have been a series of sanctions from different countries but the severe sanctions imposed in 2012 cost the country around $160 billion in revenue.

The sanction-lifting will improve the country's revenue quite dramatically but because of existing low oil prices, it might not be as much as leaders once imagined, he said.

Meanwhile, the US is copping criticism from another Kiwi academic for trying to deny Iran's prisoner release is not connected with the lifting of sanctions against the country.

Five Americans including Washington Post reporter Jason Rezaian, who was convicted on espionage charges after a closed trial, have been freed.

Otago University professor William Harris said it's a blatant lie by the US to say the prisoner release is not connected with the nuclear deal.

He said he doesn't believe for a moment that the two events are not calculatingly intertwined.

Professor Harris said there's something sordid about it, and it certainly lowers confidence in the American administration.