On Jan. 20, militants kidnapped and killed four American soldiers in a raid in Karbala, and a fifth was killed in the firefight. A U.S. defense official said one possibility under study is that Iranian agents either executed or masterminded the attack, a suspicion based on the sophisticated and unusual methods used in the attack, including weapons and uniforms that may have been American.

He spoke on condition of anonymity because the probe is ongoing.

There has been speculation that the Karbala assault may have been in retaliation for the arrest of five Iranians by U.S. troops in northern Iraq.

Those five Iranians, who were arrested in the northern city of Irbil, included two members of an Iranian Revolutionary Guard force that provides weapons, training and other support to Shiite militants in the Middle East, U.S. Ambassador Zalmay Khalilzad said last week [interesting wording in that last sentence]. Iraqi and Iranian officials maintain the five were diplomats.

Since the Karbala raid, U.S. saber-rattling has intensified. President Bush said this week that U.S. forces in Iraq would take action against Iranian operatives in the country, while insisting he had no intention of attacking Iran.

There are some reasons to think that the kidnappers at Karbala may have been Sunnis.

1. They busted up a meeting between the US military and Karbala authorities planning for security arrangements to prevent Sunni Arab guerrillas from blowing up the pilgrims in Karbala during Ashura. Why would Shiites want to interfere with those arrangements? More likely Sunnis wanted intelligence on how best to bomb Karbala then, and wanted to send a message to the Shiites that the Americans could not protect them. They probably tortured the Americans to extract what information they could from them about those arrangements.

2. They headed north to Hilla and then Mahawil. They got suspicion from Hilla police (Shiites) which shows that they weren't in cahoots with them. And they killed the US troops in Mahawil and dumped the vehicles there. Mahawil is mixed but a base for Sunni Arab guerrilla operations and part of the Triangle of Death thing. From there they could have gone north to West Baghdad and Sunni havens.

If they had been Iranians why not head east to Kut and thence to Shiite East Baghdad or on to Iran?

The one piece of the puzzle that doesn't fit is that clearly someone on the inside gave them info about the meeting in Karbala. But the Iraqi military had that info and is full of Sunnis, many of whom are double agents.

I don't actually know of any incidents in which Shiite guerrillas in Shiite areas deployed shaped charges to kill American troops. The US casualties I see in the wire services are all in Sunni areas. There are British casualties in the deep south at the hand of Shiites, but those Shiites are anti-Iranian ones like the Garamsha Marsh Arab tribe or the Sadrist splinter group of Mahmoud Hasani al-Sarkhi (which burned down the Iranian consulate in Basra).