Media playback is unsupported on your device Media caption Video shows officer body slamming girl

Texas school officials are investigating a video apparently showing a police officer body-slamming a 12-year-old girl to the ground.

Janissa Valdez's classmates are heard yelling and laughing in the footage as she is thrown by the policeman, who handcuffs her and leads her away.

She told media in San Antonio that the other children were expecting a fight between her and another girl.

The officer has been placed on leave and is yet to comment.

The incident happened late last month but the footage went viral after being posted on a local blog.

A spokeswoman for the San Antonio Independent School District, Leslie Price, called the video "alarming", saying they were still gathering all the facts but that excessive force would not be tolerated.

The girl's mother Gloria told News4SA.com: "You could just hear where she hits the ground. And it's nothing but concrete, cement.

"I talked to the officer. He did what he had to do at the moment - those were his words."

Almost 31,000 police officers are based at US public schools, recent figures show.

Last year, a school resource officer was fired in South Carolina after he was seen throwing a female student across a classroom.