UN energy watchdog to visit Iran over 'nuclear concerns'

The head of the UN watchdog on nuclear energy is visiting Iran on Sunday following concerns that Tehran has breached the terms of its nuclear agreement.

Yakiya Amano, director general of the International Atomic Energy Agency, will travel to the Islamic Republic to ensure it is honouring the historic deal brokered in exchange for sanctions relief.

"The visit is part of regular high-level contacts between the agency and Iran," the IAEA, which is policing the restrictions the agreement places on Iran's nuclear activities, said in a statement.

"In Tehran, the Director General will discuss Iran's implementation of its nuclear-related commitments under the Joint Comprehensive Plan of Action (JCPOA)," it said, using the official name of the deal.

Amano last month expressed concern over Iran's repeated testing of a limit on its stock of heavy water.

Heavy water is not itself radioactive but is used in certain types of nuclear reactor, which can in turn produce plutonium that can be used in an atomic bomb.

Iran says it has since shipped its excess heavy water out of the country, but diplomats say it has yet to be delivered to a buyer. The US and its allies say Tehran must do so to comply with the agreement.

The visit also comes as Iran is complaining increasingly loudly that the US has not held up its side of the bargain, after Congress voted to approve a 10-year extension to the president's authority to impose sanctions on Iran.

Washington insists the legislation does not violate the agreement, but allows for an "immediate snap-back" should Iran violate its deal.

In an angered response, Iranian President Hassan Rouhani on Tuesday ordered his country's scientists to start developing systems for nuclear-powered marine vessels.

According to Iran's state news agency, Rouhani ordered Ali Akbar Salehi, head of the Atomic Energy Organisation of Iran (AEOI), to work out a plan on developing nuclear power units in three months.

US President-elect Donald Trump has hinted he might tear up the nuclear agreement with Iran, but despite this Tehran has partially welcomed his election.