WARNING: Video contains coarse language.

Ottawa police have launched an internal investigation after a video was posted online showing an officer throwing several punches during an arrest.

The video shows a Jan. 29 altercation near Dalhousie and George streets in Ottawa's Byward Market.

In the video, police are seen arresting one person, who is pinned on the ground. Someone from the nearby crowd then gets involved and is quickly tackled by two officers. The video clearly shows one officer trying to punch the person at least twice.

The Ottawa Police Service's professional standards division found out about the video last week, police said, and launched an internal investigation.

Staff Sgt. Michel Marin, who is heading the investigation, told CBC News the division is trying to determine if any offences were committed.

"Like any other investigation, we go with open book, open mind and see what has occurred and see if any actions there would result in us having to address any issues with the officers or to see if any offences have been committed," Marin said in an interview over the phone.

On YouTube, the person who claims to have shot the video goes by the name Mazin and describes himself as a 21-year-old Algonquin College student.

What happened prior to the arrest isn't clear, but a person claiming to be a witness said the police were hit first.

Police said they have yet to identify the officers involved, or cross-reference the video with paperwork filed on the incident.

Police are asking any witnesses to contact them.

The Ottawa Police Service is still mired in controversy over a series of cellblock videos showing police using force against people in custody.

The case of Stacy Bonds, who was kneed and strip-searched in custody, is still being investigated by Ontario's Special Investigations Unit, which looks into cases of death, serious injury or sexual assault involving police.