Omaha Police Chief Todd Schmaderer says his department has launched an internal investigation after a video turned up online showing an officer punching a restrained man.

Police say the incident began Thursday, when officers responded to an on-going parking complaint in a north Omaha neighborhood.

Police were preparing to have some vehicles towed for expired tags when they say 28-year-old Octavius Johnson pulled up and approached officers in an aggressive manner.

But video secretly taken by a neighbor shows an officer grabbing Johnson, who does not appear combative, from behind and violently throwing him to the ground. Later, the officer is seen punching Johnson in the face several times while Johnson is prone on the ground.

Schmaderer has called a Saturday afternoon news conference to address the incident.