FORT WORTH, Texas (AP) — Fort Worth police have opened an internal investigation after video of a forceful arrest was posted by a North Texas-area activist group on Facebook.

In the 50-second video released Sunday by Next Generation Action Network , two Fort Worth officers restrain a man lying face down in the street. One officer kneels into the man's back and repeatedly punches him as the man cries, "Why (expletive) are you punching me? Why?"

Police Chief Joel Fitzgerald said in a statement Sunday that it took three officers and one supervisor to subdue the suspect. The suspect, whose name was not immediately available, was taken into custody for resisting officers.

A civil suit against Fort Worth police filed last December over a separate use of force investigation is pending.