Bush, in his speech on Wednesday unveiling his revised Iraq strategy, accused Tehran and Damascus of allowing use of their territory for launching attacks inside Iraq, and vowed "we will interrupt the flow of support."

US lawmakers voiced concern on Thursday the Iraq war could spread to neighbouring Iran and Syria if US troops were to chase militants across the border. But US officials insisted the plan was to disrupt supply lines from inside Iraq.

White House spokesman Tony Snow said he wanted to knock down an "urban legend" that Bush was "trying to prepare the way for war with either country and that there were war preparations under way."

"There are not," he told reporters. "What the president was talking about is defending American forces within Iraq."

"There's lots of war gaming," he added. "This notion that somehow the president was announcing as a precursor to planned military action, a planned war against Iran, that's just not the case."

Snow reiterated that Washington was focusing on diplomatic means against Iran over its nuclear programme. Western powers say Tehran is trying to develop nuclear weapons. Iran says it wants nuclear technology for civilian power generation.

The United States has repeatedly accused Shia Iran of meddling in Iraq, where the long-oppressed Shia majority is now in power and sectarian violence is raging. Tehran denies US charges that it supplies Shia militias with weapons.

Bush also said he had ordered an additional aircraft carrier strike group to the region and would deploy Patriot missile defence systems to "reassure our friends and allies" -- steps widely seen as a warning to Iran and Syria.

Meanwhile, recent US military raids against Iranians in Iraq were authorised by President George W Bush but do not mark a widening of the conflict, US Secretary of State Condoleezza Rice said.

She told the New York Times Bush had given an order for a broad offensive against Iranian operatives in Iraq.

"There has been a decision to go after these networks," its Web site quoted her as saying in an interview on Friday before leaving on a Middle East trip.

She said Bush issued the order several months ago after seeing increasing activity among Iranians in Iraq "and increasing lethality in what they were producing."