Washington, July 14 : Video of a Pennsylvania police officer placing his knee on a man's head and neck outside a hospital prompted protests and an investigation into the incident was underway, the media reported. In the 39-second video, shot on the night of July 11 in Allentown, Pennsylvania's third most populous city, shows three officers restraining a man lying face down on the ground and yelling, with an officer placing his knee on the man's head and neck area, reports Xinhua news agency. Allentown police said on Sunday that after the officers "interacted" with the man, he began to yell and spit at officers and hospital staff. A much longer surveillance video of the incident released later by Allentown police shows the officer using his keen twice -- the first time for eight seconds, the second for 20 seconds. On Monday, Allentown police said in a statement that they are conducting a "use of force" investigation into the incident, adding that the probe will be reviewed by the local district attorney. On Monday night, hundreds of people gathered outside the police department in downtown Allentown, holding signs and calling for the officer to be fired and police funds to be reallocated to education, mental health and other social services. Allentown's Mayor Ray O'Connell showed up and talked with protesters outside the police building to ease tensions, according to local media. The incident came amid nationwide protests against the killing of black man George Floyd in police custody in May. On May 25 in Minneapolis, police officer Derek Chauvin knelt on Floyd's neck, despite the latter repeatedly saying "I can't breathe". Chauvin, faces several charges including second-degree murder, while the other three officers - Lane, J Alexander Kueng and Tou Thao - are charged with aiding and abetting murder. /IANS