WATERLOO, Ont. -- Ontario's police watchdog says it has launched an investigation into four allegations of sexual assault involving a police force in the province.

Special Investigations Unit spokeswoman Monica Hudon says that since Jan. 1, the agency has started investigating four separate allegations of sexual assault against Waterloo regional police.

The SIU says two of the alleged incidents occurred more than 20 years ago -- one in the early 1990s and the other in October 1994.

The two other allegations involve alleged incidents that happened in September 2017 and November 2017.

Waterloo regional police would not comment on whether the allegations come from civilians or other officers.

"Waterloo Regional Police Service takes these allegations seriously, and in situations where we have received information that meets the mandate of the SIU, we have notified them accordingly," Insp. Mike Haffner said in a statement.

The force is also currently facing a proposed class action lawsuit that alleges women on staff have been subjected to sexual advances, career sabotage and personal attacks during their time on the force.

The Waterloo Police Services Board has said it views the proposed class action as "inappropriate" and said it will challenge the suit. None of the allegations have been tested in court.