Iraqi officials say 11 of their soldiers have been killed in a roadside bomb attack north of Baghdad.

The soldiers were killed as they patrolled Saturday, in a town north of the restive city of Baquba.

In a similar attack on Thursday, 10 American Marines were killed and 11 wounded near the western city of Fallujah.

In another development, the U.S. military says Iraqi and U.S. forces captured 18 suspected terrorists during operations Thursday in various parts of north-central Iraq.

Meanwhile, insurgents holding four western peace activists hostage have threatened to kill them unless all detainees in Iraqi and U.S. detention centers are freed by Thursday. A British Muslim organization has sent a negotiator to Iraq to try to win the hostages' release.