MEXICO CITY -- A city police officer was put under arrest and is being investigated following a shooting incident Saturday that wounded a student on the main campus of the National Autonomous University of Mexico, prosecutors said.

The shots were fired after a crowd verbally and physically assaulted the officer and three others officials sent by the city prosecutor's office to investigate a student's complaint of a cellphone theft earlier this month.

The officer reported that he fired shots into the air trying to deter the crowd of about 20 people and a bullet struck a male student in the thigh, the statement said. It said the officer was being treated at a hospital for bruises and was put in custody while the incident is being investigated.

Some students said the confrontation erupted after the officer was seen taking photographs of young people at the Justo Sierra auditorium, which has been occupied by a group of anarchists.

The shooting came at a time of high tension in Mexico, particularly among young people, over the disappearance of 43 teachers college students after they were attacked by police in the southern city of Iguala on Sept. 26. University students have led many protests and rallies to demand justice in that case.

Federal officials have said gang members with links to allegedly corrupt officials and police in Iguala have confessed to killing the missing students and burning their bodies. But there has so far been no conclusive identification of any remains.