PENNSYLVANIA, USA - Two gunmen working as a team fatally shot five people - including a pregnant woman - and critically wounded two others at a backyard cookout.

A prosecutor said on Thursday (March 10) that one attacker used a rifle to shoot the victims in the head as they were driven in his direction. The gunmen fled on foot.

District Attorney Stephen Zappala said of the Wednesday (March 9) nighttime shootings, "The murders were planned. They were calculated and brutal."

The medical examiner officially ruled the death of the foetus a homicide on Thursday afternoon, bringing the fatalities in the late Wednesday night ambush attack to six. The shootings took place in Wilkinsburg, Pennsylvania, a poorer, largely blighted suburb just east of Pittsburgh known for drug trafficking and gun violence.