Buffalo, N.Y. - The Buffalo Police Department says it has launched an investigation after video posted on social media showed an officer slapping and kicking a handcuffed man as he's face-down on a sidewalk.

The department's spokesman says police became aware of the 80-second video on Friday and Commissioner Daniel Derenda immediately ordered the Internal Affairs Division to open an investigation.

The video shows several officers subduing a man on a Buffalo street at night. One of the officers then slaps and kicks the man after he's already handcuffed and prone on the sidewalk.

The video was first posted on a Facebook page belonging to a group that encourages people to videotape their encounters with local police.