The U.S. military in Iraq says soldiers detained 18 suspected militants and confiscated weapons during three raids in Baghdad.

A statement says U.S. and Iraqi forces launched the raids Thursday against networks behind roadside bomb attacks.

Also on Thursday, U.S. Defense Secretary Robert Gates said American forces face more tough fighting in Iraq as they go into areas they have not been for some time.

The top U.S. military officer General Peter Pace said insurgents want to affect the American psyche with the number of major attacks they can pull off and the amount of casualties they can cause.

In the deadliest attack against U.S. forces Thursday, a roadside bomb blast in Baghdad killed five U.S. soldiers, three Iraqi civilians, and one Iraqi interpreter.

Thousands of U.S. troops are combing areas north and south of Baghdad in stepped-up operations against al-Qaida and allied insurgents.

In other violence Thursday, a suicide truck bomber killed at least 16 people and wounded about 70 others in the northern Iraqi town of Sulaiman Beck, south of Kirkuk.

Some information for this report was provided by AP.