The new measures target the finances of Iran's Islamic Revolution Guards Corps and three state-owned banks.

US Secretary of State Condoleezza Rice said the moves were part of "a comprehensive policy to confront the threatening behaviour of the Iranians". But Iran said the latest "hostile policies" were counter to international law, and accused the US of hypocrisy.

Ms Rice has reiterated a commitment to finding a diplomatic resolution to the crisis and has offered to meet "my Iranian counterpart any time, anywhere".

The US declared the Revolutionary Guards a "proliferator of weapons of mass destruction", a reference to ballistic missiles they are allegedly developing, while their elite overseas operations arm, the Quds Force, was singled out as a "supporter of terrorism".

The US has repeatedly accused Iran of destabilising Iraq and Afghanistan, blaming the Revolutionary Guards for supplying and training insurgents.

Under Executive Order 13382, US authorities will be able to freeze the assets of, and prohibit any US citizen or organisation from doing business with the Revolutionary Guards.