WASHINGTON - The U.S. military commander in Iraq says the war effort may well get harder before it gets easier, and American casualties are likely to continue to climb.

Speaking as the Senate was passing legislation to start bringing home U.S. forces in October, Gen. David Petraeus said the war will require "an enormous commitment" by the United States.

And he said that while some sectarian killings have dropped by two-thirds in recent months, the overall level of violence in Iraq has remained largely the same.

Petraeus also gave new details on what he called "exceedingly unhelpful activities" by Iran, including links to a terrorist cell that planned and carried out the abduction and murder of five U.S. soldiers in Karbala in January.

He said U.S. troops found a 22-page document on a computer during a raid last month that outlined details of that Jan. 20 sneak attack on the provincial headquarters in Karbala. Two brothers were detained in connection with the attack. *