The Treasury said that Sanam Industrial Group and Ya Mahdi Industries Group were both controlled by the Aerospace Industries Organization, a subsidiary of the Iranian Ministry of Defense, which has already been barred under US law.

Under the Treasury action, any US assets owned by the two Iranian companies are frozen, and US citizens are banned from any transactions with them.

"As long as Iran's nuclear ambitions continue to threaten the international community, the United States will use its authorities to target Iran's efforts to sell and acquire items used to develop weapons of mass destruction and the missiles capable of carrying them," said Stuart Levey, US Treasury under secretary for terrorism and financial intelligence.

"We have now taken steps to financially isolate 13 entities tied to Iranian proliferation, and will continue to act aggressively against this grave threat," he said.

Last month, the Treasury cited four Chinese companies and one US firm as WMD "proliferators", for allegedly helping Iran's missile programme.

The US government says that among the Iranian weapons are the Fateh-110 missile, with a range of 200 kilometers (120 miles), and the Fajr rocket systems, a series of North Korean-designed rockets with ranges of between 40 and 100 kilometers.

Both systems are capable of being armed with at least chemical warheads, it alleges.

Western governments accuse Iran of seeking to develop nuclear weapons under the cover of a civilian atomic energy programme. Tehran denies the allegations.

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