Shootings at two military facilities in Chattanooga, Tennessee, left four US military personnel and the lone gunman dead and three others wounded on Thursday, authorities said.According to police, the shooting incidents, which lasted for about 30 minutes, happened around 11 a.m. at the Naval Reserve Centre and the military recruiting centrE, which are about 10 kms apart, Xinhua reported.The US Federal Bureau of Investigation has launched an investigation into what local officials described as "an act of domestic terrorism"."We will treat this as a terrorism investigation until we determine it was not," said Ed Reinhold, an FBI special agent in charge of the investigation, at a press conference. "We have not determined if it was an act of terrorism or a criminal act."Reinhold also said that Thursday's shootings appeared to be the work of a lone gunman.