Iran has met a key requirement of a nuclear deal with six world powers by completing the transfer of most of its enriched uranium to Russia, a senior unnamed Russian diplomat has said.

Under the July 14 deal, Iran must ship out all except 300kg of the close to nine tons of low-enriched uranium it has stockpiled.

Low-enriched uranium is suited to power generation but can be further enriched to arm nuclear warheads.

Its removal is a key obligation taken on by Iran under the deal, which aims to reduce its ability to make nuclear weapons - something Tehran says it has no interest in.