Calgary police have charged a man after a woman was sexually assaulted in the city core on Saturday.

400 block of Third Ave. S.W. Calgary

Police allege the 17-year-old victim was in the downtown area to meet another friend when she met the suspect who invited her to hang out with him.

When she later excused herself to use the washroom, the suspect followed her and assaulted her in the washroom of an office tower in the 400 block of Third Ave. S.W., police said.

The victim fought back and was able to get away and call for help.

Police say bystanders chased the man and an altercation ensued, but the suspect ran away.

The man was found and arrested a short time later.

The 30-year-old man has been charged with sexual assault causing bodily harm, overcoming resistance by choking and breach of recognizance.

Acting Staff Sgt. Andy Nguyen says the man is known to police and had been released on condition he report to authorities as part of the high-risk offender program.

He is being held in custody until his court apperance on Thursday.