WASHINGTON (AFP) - US Secretary of State Condoleezza Rice faced a blistering challenge in Congress over the administration's failure to provide evidence to back up allegations Iran is building nuclear weapons and fueling attacks on US forces in Iraq.

"Unproven charges against Iran's nuclear intentions are eerily reminiscent of the false charges made against Iraq before we invaded that country," said Ron Paul (news, bio, voting record), a lawmaker from President George W. Bush's own Republican Party, during an appearance by Rice before a congressional panel.

He said "unproven accusations of Iranian support for the Iraqi insurgency" were also serving as a pretext for "escalating our sharp rhetoric toward Iran."

"Pressed for proof of dramatic claims of Iranian involvement in Iraq, the administration keeps promising that they are compiling it," he said.

"This sounds like Iraq, where accusations came first and proof was supposed to come later -- only that proof never came because the accusations turned out to be false," he said, referring to now discredited allegations that Saddam Hussein's regime was building weapons of mass destruction.

US officials have been promising for weeks to make public what State Department spokesman Sean McCormack described as a "mountain of evidence" to back up US allegations about Iranian involvement in attacks on US and allied forces in Iraq.

But the proof has yet to be forthcoming.

Rice rejected suggestions the administration was exaggerating its case against Iran to pave the way for military action.

"We are not planning or intending an attack on Iran," she said.

"What we are doing is that we are responding to a number of Iranian policies both in Iran and around the world that are actually quite dangerous for our national security," she said.

Rice asserted that Iranian support for terrorism was "well known and well-understood" and included providing arms and training to the Hezbollah militia in Lebanon and backing sectarian death squads in Iraq.

She said British forces in Iraq had also linked Iran to attacks on allied forces in the country, notably with sophisticated bombs able to penetrate armored vehicles.

"I don't think any government in the world would stand by and not react to that," she said.

McCormack meanwhile rejected suggestions the administration had yet to reveal its proof of Iranian involvement in Iraq because the evidence was not strong enough to sway skeptics.

"We're going to do this on our own timeline," he said, arguing that it took time to vet the "rich fact base" pointing to Iran's guilt so as not to compromise US intelligence sources.

"There are always going to be doubters, critics, skeptics, that's fine, we accept that," he said.

"It's not going to influence us into hurrying through something that we don't think is ready or appropriate."

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