Baghdad, Iraq ? U.S. troops opened fire near a checkpoint south of Baghdad after their convoy was hit by a roadside bomb and a hospital official said Sunday at least eight people were killed in the second American attack in two days to have deadly results.

In other violence Sunday, a U.S. soldier assigned to Task Force Baghdad was killed by a roadside bomb, while a Marine was killed in action in the volatile Anbar province.

This morning, gunmen assassinated the deputy police chief of Baghdad and his son, also a police officer, an interior ministry official said.

U.S. officials said they had no information about the checkpoint shooting, which occurred overnight Saturday. Interior Ministry spokesman Col. Adnan Abdul-Rahman said a roadside bomb hit a U.S. convoy near a police checkpoint in Yussifiyah, nine miles south of Baghdad, and troops opened fire, killing two police officers and three civilians.

American commanders recently announced a change in response to roadside bombings. Rather than pushing on after the blast, they now stop and try to engage the perpetrators, who may have detonated the explosives remotely.

Hours before the attack, the United States acknowledged dropping a 500-pound bomb on the wrong house during a search for terror suspects outside the northern city of Mosul. The military said in a statement that five people were killed.

Such attacks are exactly what the United States does not want prior to national elections scheduled for Jan. 30.