A Texas police chief has vowed to conduct a thorough investigation following the suspension of officer Eric Casebolt after he was videotaped slamming a 14-year-old black girl to the ground and pulling a gun on other unarmed teens at a pool party.

The white officer's behaviour spurred fury after the incident was recorded by a teenager on his cell phone and posted to social media, reports WFAA.

"We are demanding that the officer be fired and be charged with assaulting the youth," said Dominique Alexander, the president of the Next Generation Action Network, which helped organise a rally against Casebolt and the local police.

Dajerria Becton, the girl allegedly thrown to the ground by Casebolt, told broadcaster KDFW the officer twisted her arm and grabbed her by the hair. "Him getting fired isn't enough," she said.

"Our initial reaction was to place the officer on administrative leave until we can conduct a complete and thorough investigation of the incident," said McKinney Police Chief Greg Conley. "The McKinney Police Department is committed to treating all persons fairly under the law. We are committed to preserving the peace and safety of our community for all of our citizens."

Police responded to a call Friday in the Craig Ranch community 40 miles north of Dallas about a disturbance at a pool party, said Conley. On the video, boys and girls at the scene are in swimming trunks and T-shirts or bikinis on the green lawns of the suburban community. Most lie or sit on the ground complying with police orders. One boy is heard saying: "Sir, we just came for a birthday party."

Officer pulled gun on boy

Casebolt can be heard telling a group of girls to "get your ass home." After he apparently argues with Becton, he appears to throw her to the ground as other teens scream, and he pulls his gun on a group of boys who approach.

The boys run and other officers rush to Casebolt's side and yank back his gun arm. He then kneels on Becton as she cries and pleads with the other teens to "call my Mama."

"I don't know if the officers really thought about the perspective that it was showing that the people that were being order to the ground were people of colour. All the white people were kind of walking around – not being talked to. Not being yelled at," Pete Schulte, a Dallas defence lawyer who was also a reserve McKinney officer for four years, told WFAA.

Police cars were patrolling outside the police station on Monday 8 June after officers received death threats and became increasingly concerned about backlash from the video.

Casebolt was sued in 2008 by Albert Earl Brown Jr. for excessive force and racial animus after Brown said the cop and two other officers pulled down his pants and made disparaging remarks about white girls hanging out with a "dope dealer." Brown's case was dismissed in 2009.