'Echoes of Iraq'

Paul was speaking as Rice presented the US state department's annual budget request to the congressional foreign affairs committee on Capitol Hill in Washington on Wednesday.

"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.

Paul referred to discredited allegations that Saddam Hussein's regime was building weapons of mass destruction.

US officials have promised to make public what Sean McCormack, a state department spokesman, described as a "mountain of evidence" to back up allegations about Iranian involvement in attacks on US and allied forces in Iraq.

No such evidence has yet been put forward by the administration.

'No Iran attack plan'

Rejecting Paul's suggestions, Rice said: "We are not planning or intending an attack on Iran.

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

Rice also said that Iranian support for "terrorism" was "well known and well-understood", referring to Hezbollah in Lebanon and 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 armoured vehicles.

'No hurry'

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

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

"We're going to do this on our own timeline," he said.

"There are always going to be doubters, critics, sceptics … That's fine, we accept that."

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