The US announced on Thursday that it is imposing new sanctions against Iran, charging that Tehran supports terrorism in the Middle East, exports missiles and is engaging in a nuclear buildup.

The sanctions will be imposed against Iran's defense ministry, its Revolutionary Guard Corps and more than 20 Iranian companies, banks and individuals.

Under US laws, any assets found in the US belonging to the designated groups must be frozen. Americans are also forbidden from doing business with them.

The sanctions are believed to be the toughest Washington has levied against Iran since the 1979 takeover of the US Embassy in Tehran. Secretary of State Condoleeza Rice, who was joined at a State Department news conference by Treasury Secretary Henry Paulson, described the US sanctions as "a comprehensive policy to confront the threatening behavior of the Iranians."

They will "provide a powerful deterrent" for companies in the US and abroad to sever business relationships with Iran, she said.

On Wednesday, Rice told Congress that Iran poses "greatest challenge" to American security, its interests in the Middle East and around the world.

The accusation and latest sanctions came days after US President George W. Bush warned that a nuclear-armed Iran evoked the threat of "World War III," and Vice President Dick Cheney attacked the Islamic republic's nuclear drive.

Despite the tougher action against Iran, Rice insisted that the US remains open to "a diplomatic solution."

Tensions are growing between the US and Iran over Washington's accusations that Iran is secretly developing nuclear weapons and helping Shiite militias in Iraq that target US troops. Iran denies the charges.

(Xinhua News Agency October 26, 2007)