Iran's supreme leader Ayatollah Ali Khamenei has warned candidates in the US presidential election against questioning the Islamic republic's nuclear deal with world powers, his official website reported on Tuesday.

"We do not violate the nuclear accord... candidates in the American presidential election are threatening to tear up the nuclear deal. If they do so, we will burn it," he told visiting dignitaries.

Republican candidate Donald Trump has called the nuclear agreement "catastrophic".

In March, Trump said that if elected his first foreign policy priority would be to dismantle the deal and what he said was Tehran's global "terror" network.

The nuclear agreement signed in July last year between Iran and the P5+1 group -- the US, Russia, China, France, Britain and Germany -- came into force in January.

Under it, Iran has limited its nuclear programme in exchange for a lifting of many international sanctions.

Tehran accuses Washington of not actively promoting relations between Iran and international business, especially banks.

"The other party had to lift sanctions but has not done so. The question of banking has not been regulated... we are unable to recover oil revenues and other capital we have in other countries," Khamenei said.

"The Americans are not applying a large part of their commitments as we have done," he said.

Iran complains that major international banks, particularly in Europe, are reluctant to do business with it for fear of US punitive measures.

Foreign Minister Mohammad Javad Zarif, at the Oslo Forum in Norway where he is due to meet US Secretary of State John Kerry on Wednesday, urged Washington to lift "psychological" barriers to Iran doing business.

"I think that while on paper the US has lifted all sanctions, the psychological aftermath associated with many years of sanctions remains, and I think the US should play a more active role to remove them," he said.

Zarif said he would raise the issue when he met Kerry on Wednesday.