A manhunt has been launched by the US police on Thursday after a brutal killing of six people including a eight-months pregnant woman and her unborn child in the ambush-style attack at a backyard barbecue in Pennsylvania.

According to the police, they are looking for at least two suspects. At least six people killed and three injured in the brutal shooting on late Wednesday, in the town of Wilkinsburg, six miles east of Pittsburgh.

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Allegheny County police said that, three women and a man were killed at the scene, while one woman died during the treatment at the hospital. One woman among the the victims was pregnant, police Superintendent Charles Moffatt later said.

The medical examiner's office "officially determined that the eight-month-old fetus was also a homicide," he said. "So now we're up to 6 homicides at this point."

Moffatt said that, most of the victims suffered multiple wounds .The injured were "still in very critical condition," he added. The five adults killed were African-Americans aged between 25 and 37 years."They are related, cousins and a set of sisters," Moffatt added.

"It appears it was targeted," Moffatt said of the shooters' motives.

Nandini