President George Bush has sought to play down suggestions of a strike against Iran amid tension over Tehran's alleged involvement in Iraq's violence.
The US accuses Iran of fomenting violence in Iraq
US officials have recently displayed what they say is proof Iran is giving weapons to Shia militias in Iraq.
Democrats say they see parallels with the run-up to the Iraq war, when the US made a case for action on the basis of weapons which were never found.
But Mr Bush dismissed such speculation of an attack as "noise" by his critics.
"I guess my reaction to all the noise about, you know, 'he wants to go to war', is first of all I don't understand the tactics, and I guess I would say it's political," he told CSPAN television.
There is currently tension between Iran and the US on two issues - in addition to the allegations of its support to Iraqi insurgents, Washington accuses Tehran of seeking to build a nuclear weapon.
Tehran denies both charges, and argues that it is seeking nuclear power solely for peaceful, energy-related purposes.
'Excuse to stay'
On Monday, Iran's President Mahmoud Ahmadinejad said in an interview with US TV that he thought the possibility of an attack was "very low".
"We think there are wise people in the US who would stop such illegal actions," he said, stressing nonetheless that Iran's position was clear.
"Anyone who wants to attack our country will be severely punished."
He was also asked repeatedly about Iran supplying weapons to Shia militias.
He said the accusations were "excuses to prolong the stay" of US forces and that they would need a "court to prove the case".
Democratic Senator Chris Dodd said the Bush administration had tried to falsify evidence before following a briefing in Baghdad in which the alleged weapons - capable of destroying a tank - were put on display.
"I don't doubt that Iran has been involved to some degree and clearly that's a problem that needs to be addressed, but I'm getting uneasy that they're trying to create a premise, set a premise, for some future, broader military action in Iran," said Mr Dodd.
But the US allegation found some support in London. A spokesman for UK Prime Minister Tony Blair said: "We keep finding the weaponry which we don't believe to be sourced from anywhere else."