The United States is investigating whether Iran was involved in an attack on a US compound in Karbala, Iraq, which killed five American soldiers, with President George W Bush stressing that the Iranian threat was taken "very seriously".
"We take their threats very seriously. And we've got several serious issues with the Iranian government," Bush said in an interview with Fox News without directly addressing the Karbala attack.
He also reiterated that America will protect its troops.
"I've made it very clear that we will protect our troops and protect innocent Iraqi people," Bush remarked.
Meanwhile, State Department Spokesman Sean McCormack called the January 20 attack, where men wearing uniforms resembling those of US troops stormed a building housing a Joint Provincial Coordination Centre, as "notable" and that the Pentagon is investigating it.
"Clearly, the Department of Defense is looking into this particular attack. It was a tragedy. American soldiers lost their lives. And we want to understand who is responsible and how it happened, absolutely," McCormack said.
The attackers, who used US-style weaponry, uniforms and documents, are suspected by the US to be Iranians or fighters taught by Iran.
"The attack was notable... For the fact that it was highly organised. I don't think the Department of Defense has come to any conclusions as to who exactly is responsible for the attack and what, if any role Iranian agents may have played in it.
"I'm not trying to dissuade you from the point that that may well end up being the case. But I don't think anybody at this point can tell you that that is, in fact, the case now," McCormack said.
"We do know that... That the Iranian regime is engaged in supplying militias, they are engaged in training militias. I can't say that any of those activities relate to the people who perpetrated this attack," he said.
In his interview with Fox news, the president called for a united stand by the world to dissuade Iran from its nuclear ambitions, saying countries need "to work in concert" in sending a serious message.
"... There's been a Chapter 7 resolution out of the United Nations. Some in America say: Does that matter?
Well, I think it's beginning to matter to the Iranians that they're becoming isolated, that they're missing economic opportunity, that their economy and their country could do better if they weren't isolated by the world," Bush said.
"And so we're spending a lot of time keeping that diplomatic initiative strong and clearly stating to the Iranians: You don't need a nuclear weapon. But this is a serious problem, and we take it seriously," he said.