The White House has claimed Iranians are aiding fighters in Iraq and insisted the US has the authority to pursue them because they "put our people at risk."
"We are going to need to deal with what Iran is doing inside Iraq," national security adviser Stephen Hadley said.
Earlier Sunday, the US military in Baghdad said five Iranians arrested in northern Iraq last week were connected to an Iranian Revolutionary Guard faction that funds and arms insurgents in Iraq.
Raids that President Bush has approved against Iranian targets in Iraq are part of broad efforts to confront Tehran's aggression, Secretary of State Condoleezza Rice said Saturday while in Jerusalem.
President Bush's revised war strategy seeks to isolate Iran and Syria, which the US has accused of fueling attacks in Iraq. The president also says Iran and Syria have not done enough to block terrorists from entering Iraq over their borders.
"We know there are jihadists moving from Syria into Iraq. ... We know also that Iran is supplying elements in Iraq that are attacking Iraqis and attacking our forces," Hadley said.
"What the president made very clear is these are activities that are going on in Iraq that are unacceptable. They put our people at risk. He said very clearly that we will take action against those. We will interdict their operations, we will disrupt their supply lines, we will disrupt these attacks," Hadley said.
"We are going to need to deal with what Iran is doing inside Iraq."
Iran's government denied the five detainees were involved in financing and arming insurgents and said they should be released.
Hadley asserted that if Iranians in Iraq "are doing things that are putting are people at risk, of course we have the authority to go after them and protect our people."
Hadley sidestepped a question about whether US forces would move across the border to pursue Iranians who are helping Iraqi insurgents.
He said the priority "is what's going on inside Iraq. ... That's where we're going to deal with his problem."
He added, "Anytime you have questions about crossing international borders there are legal issues. ... We intend to deal with it by interdicting and disrupting activities in Iraq sponsored by Iran," Hadley said.
AP