WASHINGTON, Feb. 1 (Xinhua) -- It's almost four years into the war in Iraq, and many Americans do not even know who the enemy is.

    But the Pentagon doesn't know much about it either, according to a report from Thursday's Boston Globe.

    In an interview with the newspaper, Paul Pillar, a Pentagon official, said the U.S. military is tracking at least 28 Iraqi militias, but knows little about their leadership or command structure.

    "It is very difficult to get a handle on all of the contours of the current situation in Iraq," he said.

    "This is a civil war on top of an insurgency on top of other conflicts. There is no one simple split between side A and side B. There are numerous subgroups and splinter groups that make it difficult to say any one leader is in charge of those who come under one label."

    Last weekend's battle against the heavily armed Soldiers of Heaven killed at least 200 people in Iraq, and the intensity of the battle, and the sophistication of the group's weapons, surprised US and Iraqi forces.

    However, U.S. military and diplomatic officials said they had never heard of the group.

    Meanwhile, U.S. intelligence officials are drafting a new National Intelligence Estimate assessing all the known militia groups that could threaten Iraq's security.

    The Officials said they hoped to deliver the report to the White House and Congress in the coming weeks.