Authorities say a former US soldier suspected of killing four people at a Montana bar is still at large and believed to be armed.

Parts of a national forest near Anaconda, Montana, were closed late Saturday as authorities expanded their search for the gunman accused of killing four people at a bar on Friday morning.

The search for Michael Paul Brown, the suspect in the deaths of a bartender and three patrons at Owl Bar, continued into the weekend. Authorities have warned that he is armed and dangerous.