Four people were killed in a shooting at a Montana bar and law enforcement are searching for a suspect described by his niece as a former U.S. soldier who struggled to get help for mental health problems.

A suspect is on the run after multiple people were shot in the US state of Montana, authorities say. The Bureau of Alcohol, Tobacco, Firearms and Explosives (ATF) said it was "responding to a shooting where multiple parties have been shot at a business in Anaconda, MT".