The Treasury's move bars US banks or any American citizens from conducting any financial transactions with the two Iranians, named as Mohammad Qannadi and Ali Hajinia Leilabadi.

It also empowers the US government to freeze any assets the two men may hold under US jurisdiction.

The clampdown comes a day after Treasury Secretary Henry Paulson urged US allies to help cut off Iran's banks from the global financial system, accusing the Iranian Revolutionary Guard of funding and training Middle East militant groups.

The Treasury said it had also blacklisted three Libyan men it said were members of both Al-Qaeda and the Libyan Islamic Fighting Group.

Treasury officials signalled Friday that they were broadening a push against Iran's banks to include individuals apparently linked to Tehran's nuclear programs.

"Even individuals who are active in Iran's nuclear program are going to be held to account for their conduct and isolated by the international financial community," said Stuart Levey, who heads up the Treasury's anti-terror and intelligence operations.

The department said its move against the two Iranians was taken under presidential authority aimed at freezing the assets of "proliferators of weapons of mass destruction and their supporters."

Washington has accused Tehran of seeking to develop nuclear arms, although Tehran says its nuclear programs are for peaceful purposes.

The UN Security Council has imposed sanctions on Iran aimed at getting Tehran to suspend uranium enrichment, which makes nuclear reactor fuel but can also produce atom bomb material.

The Treasury said Mohammad Qannadi acts or purports to act for the Atomic Energy Organization of Iran which it said oversees Iran's overall nuclear program.

The department said Ali Hajinia Leilabadi serves a similar role with the Mesbah Energy Company which it said had tried to procure materials for Iran's heavy water reactor project.

Treasury described the three Libyans it had locked out of the US financial system as "terrorists" engaged in military training and procurement.

It identified them as Nur Al-Din Al-Dibiski, Sa'id Yusif Ali Abu Azizah and Ali Sulayman Mas'ud 'Abd Al-Sayyid, but said they each had many aliases.

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