Chicago police say an officer responding to a domestic disturbance shot and killed two people.

The Chicago Police Department said in a statement that the shootings happened at about 4:25 a.m. Saturday after responding officers "were confronted by a combative subject" on the city's West Side.

Police said the shooting is under investigation and the case has been referred to the city's main police oversight agency.

Independent Police Review Authority spokesman Larry Merritt confirmed Saturday that the agency was investigating but had no further information. The race of the officer and those fatally shot were not disclosed.

The Chicago Police Department is the subject of a federal civil rights investigation, which came after the release of a video showing a white officer shooting a black teenager 16 times in 2014.