The Philadelphia mayor says the actions of a throng of police officers, shown on videotape punching three shooting suspects during a traffic stop, were "inappropriate".
A sergeant and five officers have been removed from street duty as the authorities investigate the footage shot by a television crew from a helicopter.
Michael Nutter was interviewed by ABC's Good Morning America on Thursday and said: "It absolutely shows inappropriate behavior.
"There is a way to take people into custody ... and there [are] not acceptable ways of taking people into custody."
The video shows more than a dozen officers stopping the car of suspects while investigating a triple shooting on Monday night.
Charles Ramsey, a police commissioner, said investigators are enhancing the tape in order to identify how many police officers were striking the suspects.
Information will be sent to prosecutors, who will determine whether to press charges.
Ramsay said no weapons were found within the car or on the suspects, but officers said they had seen them shoot three people moments earlier.
Kicks and punches
The video shows three police cars gathering around the vehicle and officers pulling three men out.
About half a dozen officers held two men on the ground on the driver's side.
Both were kicked repeatedly, while one was punched; one also appeared to be struck with a baton.
On the other side of the car the video shows more officers kicking a third man who ends up on the ground.
Police said the three suspects - Dwayne Dyches, Brian Hall and Pete Hopkins – have all been charged with attempted murder.
D Scott Perrine, a lawyer for the three men seen in the video, has said that Dyches had head and leg injuries but he did not know the extent of the other men's injuries.