MOSCOW, Nov 23 (Reuters) - President Vladimir Putin has eased an export ban on nuclear equipment and technology to Iran, a Kremlin decree published on Monday showed, after Tehran struck a deal with world powers on its nuclear programme in July.

The decree, issued on the same day as Putin arrived in Iran on an official visit, said Russian firms were now authorised 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 modernise its Arak heavy water reactor.

The decision follows a landmark deal between six world powers and Tehran in July, under which Iran agreed long-term curbs on a nuclear program that the West has suspected was aimed at creating a nuclear bomb.

The deal will lift international sanctions on Iran in exchange for at least a decade of curbs on the country's nuclear activity including reducing the number of centrifuges used to enrich uranium, and its enriched uranium stockpile.

Putin, who will attend a summit of gas exporting countries on Monday in Tehran, is also expected to meet Iranian President Hassan Rouhani and to discuss the Syria conflict.

(Reporting by Lidia Kelly and Maria Kiselyova; Editing by Andrew Osborn) ((maria.kiselyova@thomsonreuters.com; +7 495 775 1242; Reuters Messaging: maria.kiselyova.thomsonreuters.com@reuters.net))