The Chicago Police Department warned its officers Monday about gangs armed with rifles, after three people were shot to death over the weekend and two officers were targeted in an ambush last week.

Anthony Guglielmi, a police spokesman, said three people who were killed in shootings Sunday were all members of the same street gang. Two of them died while attending a memorial for the earlier victim.

Given the very real possibility that the gang war has not played itself out, the department has saturated the same area with officers and tactical teams, Guglielmi told Fox News. It also has issued a warning about gunmen with weapons powerful enough to pierce bullet-proof vests.

Prosecutors said Monday that a reputed gang member sprayed a police van with more than two dozen rounds from a rifle after mistaking the vehicle and plainclothes officers inside for rival gang members. Authorities arrested the alleged driver in the ambush, Angel Gomez, but not the shooter. The shooting occurred in the Back of the Yards neighborhood, where two officers were shot last week.