Two US police officers have been suspended without pay after a video showed them shoving a 75-year-old man to the ground.
The footage emerged as protests over the killing of George Floyd continued into their tenth night.
The elderly man can be seen approaching a line of officers wearing riot gear in Buffalo, New York, on Thursday.
One officer pushes the man with a baton before a second man shoves him with his hand.
The sound of a crack is heard as the man falls backwards and hits the ground and blood trickles from his head.
Footage shows the majority of the officers march past after the man falls.
The officer who pushed him with a baton starts to lean over him before he is motioned away by a colleague.
Someone is heard calling for a medic.
The video was captured by a reporter from the local public radio station WBFO and was posted on Twitter.
The radio station reported that two medics came forward and helped the man into an ambulance.
Police later said that a man had been injured after tripping and falling, the radio station said.
Buffalo Mayor Byron Brown said the man was in stable but serious condition at Erie County Medical Center Hospital in the city.
Mr Brown added that Police Commissioner Byron Lockwood ordered an investigation and suspended the two officers after seeing the video.
The mayor said in a statement: "I was deeply disturbed by the video.
"After days of peaceful protests and several meetings between myself, police leadership and members of the community, tonight's event is disheartening."
The officers' behaviour attracted widespread condemnation on social media as protesters returned to the streets of several US cities to demonstrate against police brutality.
Mr Floyd died after police officer Derek Chauvin knelt on his neck for nearly nine minutes during an arrest.
New York Governor Andrew Cuomo said on Twitter that he spoke with the Mayor Brown and agreed that the officers involved should be suspended, pending a formal investigation.
He wrote:"Police Officers must enforce - NOT ABUSE - the law."