The head of the United Nations nuclear watchdog says Iran is complying with the 2015 deal with major world powers aimed at preventing the country from building nuclear weapons.

Yukiya Amano made his assessment in a regular update to the International Atomic Energy Agency's board of governors, confirming a confidential report distributed to member states last month.

He said on Monday that "Iran is implementing its nuclear-related commitments under the Joint Comprehensive Plan of Action," referencing the official name of the 2015 deal.

Amano added that "it is essential that Iran continues to fully implement those commitments."

The US unilaterally withdrew from the deal last year and re-imposed sanctions.

The other signatories Germany, France, Britain, Russia and China are trying to keep alive the deal, which offered Iran economic incentives.

Iran's supreme leader has cautioned the country's government not to pin its hopes on Europe as Tehran's nuclear deal with world powers founders under US pressure.

Ayatollah Ali Khamenei's website quoted him on Monday as saying the landmark 2015 nuclear deal "could not fix our economic problems."