The United States is planning to take advantage of domestic unrest in Iran and a slowing of the country’s nuclear programme to introduce tough new sanctions on Tehran.

President Barack Obama plans to focus fresh sanctions on Iran’s Revolutionary Guard, the military force that oversees its pursuit of nuclear weapons.

The Revolutionary Guard has also been prominent in the recent crackdown on anti-government demonstrators. Mr Obama gave Iran a deadline of the end of 2009 to make progress on complying with United Nations resolutions and suspending its uranium enrichment programme.

Tehran has not been daunted by previous sanctions but an Obama administration official said the current turmoil in Iran granted “a window to impose the first sanctions that may make the Iranians think the nuclear programme isn’t worth the price tag”.

The administration believes that Iran’s hopes of secretly enriching uranium have faltered since the disclosure in October of a secret enrichment plant under construction near Qom, the Shia Muslim holy city.

Iran suffered a second setback when international nuclear inspectors reported that the number of machines operating at the Natanz plant, used to enrich uranium for nuclear fuel, had dropped by 20 per cent since the summer because of technical problems.

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