Just when you thought the situation in Iraq couldn't get worse, the United States is now engaged in a war between the country's primarily Shiite government and the Shiite Mahdi Army of cleric Moqtada al-Sadr.

The immediate prize in the battle is Basra, Iraq's second-largest city and its major petroleum center. Basra also controls access to Iraq's only outlet to the sea.

The contesting forces are the occupation government of Prime Minister Nouri Kamal al-Maliki and the army and other security forces that the United States has been training, and various Shiite militia forces, the largest of which is the Mahdi Army, under the leadership of Mr. Sadr. The Mahdi Army had been observing a cease-fire for months at his instructions.

The al-Maliki government has gone after them in Basra because the extent and corrupt nature of their role in that area and among the majority Shiites across the country constituted a major challenge to the authority of the al-Maliki government and its American sponsors.

The fighting has gone on for days. Iraqi government forces have not succeeded in defeating the Mahdi Army, and now Mr. al-Maliki has extended the initial three-day period during which they were supposed to disarm to April 8, a setback for him.

American forces have now weighed in on the side of the unsuccessful government forces, bombing Basra and other targets. A curfew also has been declared in the capital, Baghdad. Some Iraqi police are stripping off their uniforms and joining the Mahdi Army.

This battle is not even Sunnis vs. Shiites. Nor does it involve al-Qaida in any way. It is an intra-Shiite conflict, a sort of sub-civil war. These battles can go on quite a while, as was the case in Lebanon in the 1980s when the Shiite Amal movement fought the Shiite Hezbollah for years.

Americans continue to die in Iraq. America's money continues to be poured into Iraq. With this new internal war that the United States has joined, its engagement has reached a new level of craziness.