The United States today imposed its harshest programme of sanctions on Iran since the Islamic Republic's 1979 revolution.

Condoleezza Rice, the Secretary of State, announced that 22 Iranian Government agencies and three state-owned banks were being blacklisted, in an attempt to punish Iran for refusing to stop enriching uranium.

In particular, the sanctions target Iran's elite Quds Force, a military unit which the US says helps to train worldwide Islamist militant groups, as well as its Revolutionary Guards.

Announcing the measures, Ms Rice told journalists: "These actions will help to protect the international financial system from the illicit activities of the Iranian government.

"They will provide a powerful deterrent to every international bank and company that thinks of doing business with the Iranian Government."

The Secretary of State, who yesterday described Iran as the single greatest challenge to US security, added that America was committed to resolving the crisis through diplomatic means.

However, she gave warning: "If they choose to continue down a path of confrontation, the US will act with the international community to resist these threats of the Iranian regime."

There was no immediate reaction from Iran, but a leading Iranian MP immediately dismissed the new sanctions as a "strategic mistake."

"This will make the wall of distrust between Iran and the United States higher every day and will close down dialogue," Kazem Jalali, spokesman for the Iranian Parliament’s foreign affairs and security commission, told the AFP news agency.

Times Recommends

• How the fall of the Wall freed Nelson Mandela
• Iguacu, the world’s most spectacular waterfall
• How Harrods helped Burmese cats return