WASHINGTON - An off-duty police officer accused of putting his knee on a 12-year-old girl's neck to restrain her amid a lunchtime fight in Kenosha in the Midwest US state of Wisconsin, is under investigation, NBC has reported, citing the city's police department.

The surveillance footage released on Friday by Kenosha Unified School District shows that Kenosha officer Shawn Guetschow, who was working as a security guard at the school, intervening in a fight on March 4 by placing his knee on the girl's neck for half a minute to subdue her, NBC reported on Tuesday.

Jerrel Perez, the girl's father, has called for criminal charges against Guetschow for using a type of restraint that was banned for Wisconsin law enforcement officers last year. Perez said his daughter is in therapy and seeing a neurologist for her injuries.

Guetschow resigned from his security guard post with the school on Tuesday, but remains employed by the city police force, Kenosha Police Department tweeted.