A protest against police brutality took a violent turn Tuesday as demonstrators clashed with police.

Several people were arrested as protesters made their way from Union Square over the Brooklyn Bridge at the Stop Mass Incarceration Network's "National Shut Down."

Police say at least one officer, who was off-duty, was attacked by a protester during the march.

They're also investigating whether a second officer may have been hit with a bottle.

Protesters say they were responding to police killings around the country, including the recent shooting death of an unarmed man in South Carolina.

"Look at these pictures on the banner. These are just a few of the hundreds of people killed every year by the police. The killer cops are getting away with it, and what we're saying is that that must stop, and we took to the streets to bring the movement of resistance back out into the streets to say that it must stop," said protest organizer Carl Dix.

It's not clear yet how many people were arrested

Police say the off-duty officer was taken to the hospital for injuries to his face and arm.

In a statement, Mayor Bill de Blasio said violence against police is unacceptable and will not be tolerated.