Washington: The United States is investigating whether Iran was involved in anattack on a US compound in Karbala, Iraq, which killed five American soldiers,with President George W Bush stressing that the Iranian threat was taken 'veryseriously.'

"We take their threats very seriously. And we've gotseveral serious issues with the Iranian government," Bush said in aninterview with Fox News without directly addressing the Karbala attack. He also reiterated that Americawill protect its troops.

"I've made it very clear that we will protect our troops and protectinnocent Iraqi people," Bush remarked.

Meanwhile, State Department Spokesman Sean McCormack called the January 20attack, where men wearing uniforms resembling those of US troops stormed abuilding housing a Joint Provincial Coordination Centre, as "notable"and that the Pentagon is investigating it.

"Clearly, the Department of Defense is looking into this particularattack. It was a tragedy. American soldiers lost their lives. And we want tounderstand who is responsible and how it happened, absolutely," McCormacksaid.