The FBI has reportedly launched an investigation after police officers in Missouri were seen allowing a K-9 unit to attack a restrained man.

In an email, Woodson Terrace police Chief Randy Halstead told the St. Louis Post-Dispatch that his office is "fully cooperating" with the investigation, which was prompted by a cell phone video that caused outrage online.

The video shows two officers pinning a Black man to the hood of a car while another officer approaches with a barking police dog.

"I know he ain't siccing that dog on him!" someone can be heard shouting.

Seconds later, the K-9 officer allows the dog to bite the suspect's legs. The attack continues until the man falls to the ground.

The department later defended the move in a press release.

"On Monday, 09/20/2021 at approximately 7:18 am our officers responded to a local business for a subject trespassing and refusing to leave," the statement said. "Upon the officers arrival the subject left the business and was located by the officers walking towards another business."

The statement went on to suggest that the officers suspected that the man was guilty of using narcotics.

"The officers advised the subject to place his hands behind his back but he refused and when the officers attempted to place the subjects hands behind his back the subject resisted and refused to comply," the statement continued. "The subject was then warned several times that if he did not comply the K9 would be released. The subject continued to resist causing minor injuries to one of the officers so the K9 was released and the K9 gained control of the suspect's foot. The suspect went to the ground and the K9 was pulled off the subject."

Watch the video below.

Woodson Terrace Police in Missouri let a K-9 loose on a man. Every officer here should be terminated immediately. pic.twitter.com/zgI2qHCYjo

— Fifty Shades of Whey (@davenewworld_2) September 26, 2021