BAGHDAD — At least five people were killed and 27 others wounded, including 17 policemen, in a series of coordinated explosions late Thursday that struck the city of Ramadi, the capital of Anbar province, police said.

The explosions took place at about 9 p.m., and involved at least four separate bombs, two of which appeared to have been timed to kill first responders taking victims to the hospital.

The target of the first three bombs — a car bomb, a roadside bomb and another explosive carried on a motorcylce — was the headquarters of the Anbar provincial government. When responding security forces began moving the wounded to the main city hospital, a fourth bomb, also hidden aboard a motorcycle, went off.

The use of motorcycles to hide some of the bombs was unusual.

Anbar province was once Iraq's most violent but has been relatively peaceful since Sunni Muslim tribes rebelled against insurgent groups pressing a radical Islamist agenda. But tensions have risen in recent days after a police officer was killed.

In other violence, gunmen killed a tribal sheikh in Fallujah, another city in Anbar. Sheikh Hameed Mohammed was driving though the Jolan neighborhood when he was killed.

In Baghdad ,1 3 people including two policemen were wounded by roadside bombs in four separate incidents.