Russia has moved to ban the delivery of crucial air defence missiles and other weapons to Iran.
President Dmitry Medvedev has issued a decree prohibiting the sale of the high-precision S-300 system after the UN imposed fresh sanctions in June.
The order brings trade rules for Russia and its companies into line with the sanctions.
The move is certain to please the United States and other Western nations that have expressed concern over Iran’s military capability and its nuclear programme.
But the timing of the decree could have been intended to appease the West after the start-up of a Russian-built nuclear power plant in Iran last month and the recent announcement of plans to sell missiles to Syria.