The United States can no longer win the insurgency war in Iraq militarily, according to a new report.

The Washington-based Center for Strategic and International Studies asserted in a new report that the United States no longer has a military solution for Iraq. Authored by Anthony Cordesman, the report said any U.S. military solution would result in massive civilian casualties and collateral damage and fail to end the Shi'ite or Sunni insurgency.

"The U.S. can of course defeat the Iraqis," the report said. "However, any military solution is now likely to be the kind of 'victory' that creates a new firestorm over excessive force, civilian casualties, and collateral damage. At the same time, the U.S. cannot hope to kill or arrest all of the Sunni and foreign insurgents that exist now and is almost certain to create far more than it destroys."

On Thursday, a suicide attacker blew up a car full of explosives near a checkpoint to the U.S. headquarters in Baghdad. Six Iraqis and a U.S. soldier were killed, Middle East Newsline reported. At the same time, Iraqi insurgents destroyed the headquarters of the pro-U.S. Patriotic Union of Kurdistan in Baaquba.

Earlier, U.S. troops launched what was termed the largest military operation against Sadr in Karbala and Najaf. At least 15 Iraqis and a U.S. soldier were killed.

The report discussed Iranian-backed cleric Moqtada Sadr, head of the Mahdi Army, and warned against any U.S. attempt to assassinate him. The killing of Sadr, the report said, would create a martyr that would push Shi'ites into an alliance with the Sunnis in a development that would ensure nationwide resistance.

"At this point, there simply is no way to eliminate cadres of insurgents or to disarm the most threatening areas," the report said. "Falujah and similar areas have too much popular support for the insurgents. There are too many arms that can be hidden and too many points of vulnerability. This does not mean the U.S. should give up fighting the insurgents or its efforts to disarm them. It does mean the U.S. must accept that it cannot win in the sense of eliminating them or turning hostile areas into secure and disarmed areas."

Cordesman, who completed a tour of the Middle East, said the United States lacks viable options other than to empower Iraqis with responsibility over security. He played down the prospect that the United Nations could create stability or political legitimacy.

Other U.S. options cited by the report included the acceleration of U.S. aid to the Iraqi military and security forces as well as the search for Arab military training and support. Such an effort must include the provision of a broad-based Iraqi military command.

"Forget contract regulations on buying equipment," the report said. "Deliver everything necessary and worry about the details later."

Another recommendation was that U.S. military commanders should be empowered to approve security aid to Iraq. At the same time, Washington should threaten to leave Iraq if an interim Iraqi leadership fails to cooperate in the effort to form a stable and efficient government.

The United States should also continue to expand the role of the Iraqi security forces. At the same time, the report said, the United States should not repeat the "Israeli mistake of assuming that any Iraqi authority in hostile areas can be counted on to provide security for Americans."