Three police officers were shot and killed in an ambush as they drove through a run-down Bologna neighborhood, authorities said Saturday.

The Carabinieri policemen, all in their early 20s, were patrolling a dark, secluded section of the city late Friday night when their car was blocked by four large garbage containers.Investigators said a white car pulled alongside the patrol car and an unspecified number of assailants opened fire with pistols and at least one machine gun, killing the three policemen.

The car was later found abandoned and burned several miles away.

Investigators said the motive for the attack remained unclear.