Hundreds of people have marched to a swimming pool where a police officer was filmed pointing his gun at teenagers.
The video, filmed on Friday, shows an officer in McKinney, Texas pinning a black 15-year-old girl in a bikini to the ground with his knees.
The protesters are demanding that the police officer, who is white, should be dismissed.
The officer, Corporal David Eric Casebolt, has been placed on leave.
In a statement posted on Facebook, McKinney police said they were called because a number of uninvited people refused to leave the swimming pool. A fight then broke out, and more calls were made to police.
In a video that is more than seven minutes long, Mr Casebolt is shown swearing at a number of black youths, pointing his gun at others, and pulling the girl by her arm, before pinning her to the ground with his knees.
“Call my momma!” the girl screams several times as she struggles with the officer.
The girl, Dajerria Becton, told the Texan broadcaster KDFW: “Him getting fired isn’t enough.”
On Monday night, close to 800 people marched through McKinney, a city of almost 150,000 people.
They walked from a school to the swimming pool, carrying placards with slogans including “My skin colour is not a crime” and “Don’t tread on our kids”.
Civil rights leaders in McKinney said they wanted an investigation by the US justice department, and to see Mr Casebolt dismissed.
Police said the video “raised concerns that are being investigated”.
Mr Casebolt has not commented on the investigation. He remains in hiding, according to US media reports.