The U.S. military in Iraq says six American soldiers were killed in separate incidents over the past two days

The military said four soldiers were killed and two others wounded in a roadside bomb explosion Thursday in eastern Baghdad, where two bombs went off as the soldiers were returning from a search operation. The second explosion caused the U.S. casualties.

Also on Thursday, one soldier died of injuries sustained during combat operations in Salah ad Din province, north of Baghdad.

And, a U.S. Marine died Wednesday in a non-combat related incident in the restive Al Anbar province.

In other violence, a car bomb killed at least four people and wounded 24 others Thursday in the town of Iskandariyah, an area south of Baghdad that has been hit frequently by Sunni Arab insurgents,

And the U.S. military says it is investigating an incident Wednesday in the northern city of Mosul, in which coalition forces killed an Iraqi soldier by mistake. An initial account indicates that coalition ground forces and a helicopter were fired on during a raid in Mosul, and they returned fire, killing one person who was later identified as a member of the Iraqi army.