Baghdad, Iraq ? Between three and six American soldiers are killed and another 40 wounded every week in Iraq by an enemy that has become more lethal and sophisticated since the fall of Baghdad in April, the commander of coalition forces said Thursday.

Nearly six months after the fall of Baghdad, U.S. soldiers are still facing 15-20 attacks a day, including roadside bombs, Lt. Gen. Ricardo Sanchez said. Seven to 10 attacks a day involve small groups of fighters.

“They’re getting attacked every day,” Sanchez said of his soldiers. “I’m having soldiers wounded at a rate of about 40 a week and getting killed anywhere from three to six soldiers a week.”

Most attacks occur in Baghdad and the surrounding Sunni Muslim stronghold to the west and north of the capital, although it’s unclear whether Iraqi or foreign forces account for the majority.

“The enemy has evolved — a little bit more lethal, a little more complex, a little more sophisticated, and in some cases, a little bit more tenacious,” Sanchez said.

Since May 1, when President Bush declared the end of major combat operations, 90 American soldiers have been killed by hostile fire in a low-level, guerrilla-style insurgency. A total of 317 Americans have died since the war began March 20, according to the Pentagon.

In Thursday’s violence, about 10 U.S. soldiers came under fire in Fallujah, 30 miles west of Baghdad, in front of the mayor’s office. No Americans were hurt but one Iraqi bystander was killed and four people, including a mother and her 4-year-old daughter, were wounded, hospital officials said.