But Rice said that President George W. Bush is backing diplomatic efforts aimed at convincing the Islamic republic to freeze nuclear activities that Washington fears are a drive to build an atomic bomb.

"This is a relationship that is, I think, increasingly difficult in a country that is increasingly dangerous," the chief US diplomat told CNBC television.

Rice outlined Washington's numerous complaints about Iran, saying it supports terrorism, backs armed militias threatening US forces in Iraq and pursues technologies "that would lead to a nuclear weapon."

She also pointed to Iran authorities' "crackdown on their own population" and arrests of people with dual Iranian-American citizenship.

"So this is a very dangerous state with very dangerous policies and we need the help and support and intensify efforts of the international community to deal with Iran," she said.

Asked about the possibility of a US military strike against Iran, Rice repeated the Bush administration's refusal to rule it out.

"Well, the president's never going to take his options off the table and frankly no one should want the American president to take his options off the table," she said.

But she added that Bush has "made clear" that he was supporting "diplomatic solutions to the Iranian problem."

The UN Security Council has imposed sanctions on Iran for its refusal to suspend uranium enrichment, which produces nuclear reactor fuel but can also be used as material for an atom bomb.

Iran insists it is running a peaceful nuclear program solely aimed at meeting its civilian energy needs.

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