"What the Iranians are doing is killing American servicemen and -women inside Iraq," said Secretary of Defense Robert Gates.
U.S. officials are also concerned by Iranian harassment of U.S. ships in the Persian Gulf as well as Iran's still growing nuclear program. New pictures of Iran's uranium enrichment plant show the country's defense minister in the background, as if deliberately mocking a recent finding by U.S. intelligence that Iran had ceased work on a nuclear weapon.
No attacks are imminent and the last thing the Pentagon wants is another war, but Chairman of the Joint Chiefs of Staff Mike Mullen has warned Iran not to assume the U.S. military can't strike.
"I have reserve capability, in particular our Navy and our Air Force so it would be a mistake to think that we are out of combat capability," Mullen said.
Targets would include everything from the plants where weapons are made to the headquarters of the organization known as the Quds Force which directs operations in Iraq. Later this week Iraqi Prime Minister Nouri al-Maliki is expected to confront the Iranians with evidence of their meddling and demand a halt.
If that doesn't produce results, the State Department has begun drafting an ultimatum that would tell the Iranians to knock it off - or else.