The added troops mean there are some 150,000 U.S. military personnel in Iraq.

The increased troop presence has led to increase casualties, U.S. military officials said, Voice of America reported. The Pentagon reported that as of Wednesday night, 115 American soldiers had been killed in May in Iraq.

"It's been a tough month," U.S. Army Brig. Gen. Perry Wiggins said Wednesday at a Pentagon news conference.

U.S. commanders in Iraq are "starting to see a shift of momentum" that includes more support from Iraqi civilians and a 50 percent drop in insurgent attacks in the western al-Anbar province, Wiggins said in the VOA report.

But in Baghdad, there has been a slight increase in attacks, Wiggins said.

Wiggins said Iraqi insurgents are still capable of large-scale bombings and small, targeted bomb attacks.

Wiggins repeated U.S. allegations that Iran is providing training and technology to Iraqi insurgents. But he said U.S. officials haven't determined which, if any, Iranian officials are behind the insurgent support.