US police are searching for two shooters and a motive after a backyard party ambush near Pittsburgh killed at least five people and injured three others.
Four women and one man were shot and killed, and another three people were wounded in Wednesday's attack, about 13km east of the city, the Allegheny County Police Department said.
Dozens of shell casings littered the pavement of an alleyway near the site, where police were gathering evidence and talking to witnesses, according to media reports.
A 41-year-old woman who was wounded in the shooting was treated and released from a local hospital, according to a hospital spokesman.
Two suspects fired from an alley onto a backyard party at a home, the police department said in a statement, then one of the shooters fired from the side or adjacent backyard as partygoers tried to run into the home. The suspects then fled.
Four died at on the back porch, while another woman died at a hospital, the police statement said.
Two males were reported in critical condition and a woman in stable condition at local hospitals.
"We do not have any suspects in custody and the motive is not exceptionally clear at this point," said Lieutenant Andrew Schurman of the Allegheny County Police Department.
The shooting in Wilkinsburg, a borough of about 15,000 chiefly lower and middle-income residents, is the latest in a series of mass shootings that have made gun control a matter of heated debate in the United States.
The shooting generated more than 10,000 tweets, with many expressing outrage over gun violence.
"Woke up to the terrible news about the Wilkinsburg shooting," US congressman Mike Doyle, who represents the Pennsylvania district that includes Wilkinsburg, said on Twitter.
"My prayers are with the families and friends of the victims."