Russian President Vladimir Putin has formally eased an export ban on nuclear equipment and technology to Iran.
The decree was published by the Kremlin on November 23, the same day as Putin arrived in Tehran on an official visit.
The Russian move comes after Iran and six world powers reached a deal in July under which Iran agreed to curb its nuclear program in exchange for the lifting of international sanctions.
According to the decree, Russian firms are now authorized to export hardware and to provide financial and technical advice to help Iran with three specific tasks.
They were listed as helping it modify two cascades at its Fordow uranium-enrichment plant, supporting Iranian efforts to export enriched uranium in exchange for raw uranium supplies, and helping Iran modernize its Arak heavy-water reactor.
In related news, Iran's ambassador to Russia said on November 23 that Moscow had started the procedure of supplying Tehran with S-300 antiaircraft systems, according to the Tasnim news agency.
Russia and Iran signed a contract for Moscow to supply Tehran with S-300 surface-to-air missile systems on November 9.
Based on reporting by AP, Interfax, and AFP