Dubai: The United States on Thursday imposed sweeping new sanctions against Iran, accusing Tehran of "threatening" Israel's security, supporting terrorism, exporting missiles and "engaging in a nuclear buildup".

The sanctions are the harshest since the two countries broke off diplomatic ties following the Islamic revolution in 1979. Targeting more than 20 Iranian companies, banks and individuals, the sanctions are likely to have ripple effects throughout the international banking community, the Associated Press reported.

US Secretary of State Condoleezza Rice, at a joint press conference with Treasury Secretary Henry Paulson, said the steps the Bush administration was taking against the Revolutionary Guard Corps and a number of banks are designed, among other things, to "punish" Tehran.

Rice said the moves were in response to "a comprehensive policy to confront the threatening behaviour of the Iranians" although she also said that Washington remains open to "a diplomatic solution".

But Rice quickly added: "Unfortunately the Iranian government continues to spurn our offer of open negotiations, instead threatening peace and security by pursuing nuclear technologies that can lead to a nuclear weapon ... supporting Shiite militants in Iraq and terrorists in Afghanistan, Lebanon and the Palestinian territories, and denying the existence of a fellow member of the United Nations, threatening to wipe Israel off the map."

The sanctions will identify more than 20 Iranian entities, particularly the Revolutionary Guards' Quds Force - which Washington accuses of providing weapons, including powerful bomb-making material blamed for the deaths of US soldiers in Iraq - will be identified as a "specially designated global terrorist" groups for their activities, US officials said.

Rice said the new sanctions will "provide a powerful deterrent" for companies in the United States and abroad to sever business relationships with Iran. The sanctions would be unilateral, however, and are believed to be the first of their type taken by the US specifically against the armed forces of another government.

'New steps are a strategic mistake'

The fresh US sanctions against Iran's Revolutionary Guards are a "strategic mistake" that will increase distrust between the two countries, a top Iranian MP said.

"The United States has committed a strategic mistake by blacklisting the Revolutionary Guards," Kazem Jalali, spokesman for parliament's foreign affairs and security commission, told AFP.

"The Revolutionary Guards is an official force in Iran and it is clear that labelling them terrorists is interfering in the domestic affairs of a sovereign nation," said Jalali.