TORONTO -- An investigation is underway into an alleged sexual assault at a prestigious private school in Toronto, police said Wednesday as the institution announced it had expelled students over two serious incidents.

Police released few details but said the investigation involved St. Michael's College School, an all-boys Catholic institution that teaches grades 7 through 12, and officers believe a video depicting an alleged assault has been circulating.

In a statement Wednesday night, police said investigators from the department's Child Exploitation Section have determined that the video "meets the definition of child pornography," and that anyone possessing a copy should delete it immediately.

The school did not immediately respond to a request for comment but said in a letter to parents that administrators became aware of "two very serious incidents" that recently occurred on campus and were in violation of the student code of conduct.

"The nature of student conduct in each case is injurious to the moral tone of the school and the well-being of our students," the school wrote. "The school has zero tolerance for such behaviour."

The school said it learned about the incidents on Monday and began an investigation that included informing police and meeting individually with the students involved and their parents.

"Swift and decisive disciplinary action has taken place, including expulsions," the school said in a separate statement posted to its website.

The school told parents it addressed the student body in a "formal assembly" on Wednesday afternoon, and would talk to Grade 9 students who were participating in Take Our Kids to Work Day on Thursday.

"Given police involvement, and respecting the privacy and confidentiality of all parties, the school will not be making any further comments at this time," it said.

A follow-up email to parents said additional support would be available for students who need it. The email from the director of student affairs said boys who need someone to talk to can approach any guidance counsellor.

The school is known for its athletic program. Alumni include hockey greats Frank Mahovlich, Dave Keon and Tim Horton. Track star and Olympic hopeful Justyn Knight also attended the school.

Provincial NDP lawmaker Jill Andrew, who represents the riding that includes St. Michael's College School, calls the reports of alleged sexual assault "deeply disturbing.

"Every student should be able to attend school in an environment where they are safe," Andrew said in a statement Wednesday evening.

"I join with my community of St. Paul's in saying that sexual violence has no place in our community."