Iran is conducting a proxy war against the United States in Iraq, declared Ambassador Ryan Crocker last week.

How? Gen. David Petraeus explained. The Quds Force of the Iranian Revolutionary Guard and Hezbollah are arming, training and directing the Shia militia fighting U.S. and Iraqi forces in Basra and firing rockets into the Green Zone. Said Petraeus, the Quds Force is responsible for killing hundreds of American soldiers.

If true, these are acts of war from a privileged sanctuary. And Bush would be as justified in attacking these Iranian base camps as was Nixon in ordering U.S. forces to clean out the North Vietnamese sanctuaries in Cambodia.

While there is no reason to question the truth of what Petraeus and Crocker allege, this proxy war raises a question. What is Tehran's motive?

Iran, after all, is the principal beneficiary of the U.S. invasion that dethroned its enemy Saddam, ended the Sunni Baath Party's monopoly of power and opened the door to Shia politicians with strong ties to Tehran. The regime in the Green Zone is the same regime that rolled out a red carpet for President Ahmadinejad.

Why, then, would Iran bloody it up? Why, when things are going Iran's way in Iraq, would it risk war with the United States over Iraq?

The April 16 Los Angeles Times offers an answer. Iran's proxy war against us in Iraq may be Tehran's response to a U.S. proxy war being waged against Iran. Ahmadinejad may be exacting blood for blood.

According to Times' writer Borzou Daragahi, Iran believes the United States is behind groups that are systematically killing Iranians along the border.

One such group is the Party for Free Life in Kurdistan, or PEJAK, which is linked to the PKK that has conducted a terrorist war in Turkey and is considered by the United States a terrorist organization. The founder of PEJAK is Osman Ocalan, brother of the founder of the PKK, who is now serving a life sentence in a Turkish prison.

As Turkey retaliates against the PKK with artillery fire and raids into Kurdistan, Iranians are now doing the same.

A second group, regarded by both the United States and Iran as terrorist, is the Mujahedin Khalq, a cult-like group, operating inside Iraq on the Iranian border. Iranians also believe the United States is behind attacks in the oil-rich and Arab Khuzestan region of southwest Iran. Continued...