Five American Marines have been killed in a roadside blast in western Iraq, US officials say.
The attack came hours after reports that 17 bodies had been found bound and killed execution-style in the same restive province, Anbar.
In Baghdad, at least three Iraqis were killed and several wounded in a car bomb attack near a busy marketplace in the mainly Shia district of Shula.
In Kirkuk and Basra, police colonels were killed in drive-by shootings.
"Five marines were killed in action Thursday when their vehicle hit an explosive device while conducting combat operations near Haqlaniyah," the US military said in a statement.
Further west, close to the Syrian border, 17 bodies were found in two separate groups near the desert town of Qaim.
Officials said 22 Iraqi soldiers were kidnapped in the area on Wednesday but it was not clear if the bodies were of some of the troops.
Eleven of the bodies had been dumped in a gravel pit.
Witnesses, including an Associated Press reporter, said the victims had their hands tied behind their backs and were wearing civilian clothes.
The discovery came a day after six bodies were found nearby, also in civilian clothes. Some of them had been beheaded, witnesses said.
The group of soldiers went missing on Wednesday after leaving their Qaim base to go to Baghdad on leave. They had been wearing civilian clothes, police said.
Al-Qaeda in Iraq, the group led by Iraq's most-wanted militant, Abu-Musab al-Zarqawi, said on a website it had captured 36 Iraqi soldiers, or "infidel guards", in western Iraq on Wednesday.
The blast in Baghdad happened near a busy marketplace at 2200 (1800 GMT), an hour before a night-time curfew came into the effect, an interior ministry source told the AFP news agency.
At least 15 people were wounded, the AFP reported.
Police in the northern city of Kirkuk said Colonel Rahim Uthman, head of the local anti-terrorist department, had been killed on Thursday.
He and his assistant Major Ghanim Jihad were shot dead from a blue BMW, they said.
And on Friday in the southern city of Basra, the commander of the local police academy was shot dead.
Three or four gunmen in a car swerved in front of Colonel Abdelkarim Daraji's vehicle and opened fire, police said. His brother also died in the attack.