More police are being deployed in Philadelphia as authorities say they fear another night of unrest after the fatal police shooting of a black man.
Thirty officers were injured during the overnight clashes with protesters, officials say.
Police say officers opened fire on Walter Wallace, 27, when he ignored orders to drop a knife he was holding.
Mayor Jim Kenney later said the video of the shooting “presents difficult questions that must be answered”.
The mayor did not elaborate, but said he was looking forward “to a speedy and transparent resolution for the sake of Mr Wallace, his family, the officers, and for Philadelphia”.
Meanwhile, Philadelphia Police Commissioner Danielle Outlaw said she had visited the scene and heard and felt the anger of the community”.
An investigation into the incident is under way.
Large protests broke out in Philadelphia earlier this year following the police killing of African-American George Floyd in Minneapolis, Minnesota. Footage showed white police officer Derek Chauvin kneeling on Floyd’s neck, while he repeatedly said he was unable to breathe.
Floyd’s death sparked protests around the world against racism and police brutality.
What happened overnight?
Hundreds of people took to the streets to protest against Monday’s shooting.
The protests, which continued into the early hours of Tuesday, turned violent at times.
Images from the scene showed a police vehicle set on fire. A number of businesses and shops were looted.
Most of the injured police officers were struck by objects such as bricks and other projectiles, authorities said.
One officer was in hospital with a broken leg and other injuries after being struck by a pickup truck.
More than a dozen people were arrested.
What do we know about the shooting?
Police said the shooting happened at about 16: 00 (20: 00 GMT) on Monday, when two officers responded to a report of a man with a weapon in the neighbourhood of Cobbs Creek in West Philadelphia.
Police spokeswoman Tanya Little told AP news agency that a man, later identified as Mr Wallace, was holding a knife when the officers approached, and instead of following orders to drop the weapon “advanced towards them”.
Both officers fired “several times”, hitting Mr Wallace in the shoulder and chest.
One of the officers drove him to a hospital, where he was pronounced dead, Ms Little said.
Footage shared on social media shows two officers pointing their guns at Mr Wallace as he walks towards them. The officers back away from him and shout at him to put the knife down.
Shots are then fired and Mr Wallace is seen lying on the street.
“Why didn’t they use a taser?” he asked.