Retired Marine Col. Gary Anderson conducted the exercises and told the newspaper three major developments unfolded in the exercise and the result was a country divided into sectarian thirds.

"It will be ugly," Anderson said of a U.S. departure in the near future.

Contracted role players with expertise in the various factions' historical behavior worked through the withdrawal scenario and showed Iraq would break down along religious and ethnic lines, the report said.

The Kurdish north separated and welcomed a U.S. presence, minority Sunnis were driven from mixed areas around Baghdad west into Anbar province and southern Iraq was forecast to erupt into civil war between rival Shiite Muslims, the newspaper said.

However, a senior Bush administration official who didn't want to be identified said while the war game was a useful exercise, it wasn't considered to be inevitable fact.

"We've got to be very modest about our predictive capabilities," the official told the Post.