NIAGARA FALLS, Ont. -- Police say a Niagara Falls, Ont., high school teacher is facing charges in a sexual assault investigation.

Niagara Regional Police say the investigation began last December following reports on inappropriate sexualized behaviour by a 31-year-old male teacher involving two female students under 18 years of age.

Detectives determined that one of the girls was a student at the school where the teacher worked beginning in 2013, while the second girl was a student of a St. Catharines, Ont., school where he taught from 2009 to 2013.

Investigators say Michael J. Molnar of Pelham, Ont., is charged with two counts of sexual assault, and one count each of sexual interference, invitation to sexual touching, and sexual exploitation.

The allegations stem from incidents on and off school property, and during and after school hours, and detectives say the investigation continues.

Molnar is to appear for a bail hearing on Tuesday in a St. Catharines court.