WASHINGTON, July 16-- Shootings at two military facilities in Chattanooga, Tennessee, left four U.S. military personnel dead and three more wounded Thursday. The gunman was later also killed, authorities said.

According to local police, the two shooting incidents, which lasted for about 30 minutes, happened around 11:00 a.m., local time, at a military recruiting center and the Naval Reserve Center about 10 kilometers apart. The shooter reportedly shot while driving in an open-top Mustang.

The U.S. Federal Bureau of Investigation has already started its 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."

The Washington Post earlier quoted senior FBI officials as saying that the shooting did not appear to be related to any terrorist group.

Meanwhile, Reinhold said that the gunman, with "numerous weapons" on him, appeared to act alone, adding that the gunman did not work at the military facilities involved.

TV network CBS News quoted U.S. law enforcement officials as saying that the suspect shooter was Muhammad Youssef Abdulazeez. Earlier Thursday, local police said the suspect was believed to have lived in the area and acted alone.

The shooting incidents came one month after a racially motivated white gunman shot dead nine African-American churchgoers in Charleston, South Carolina. The authorities was initially investigating the Charleston church massacre as "hate crime," rather than a possible act of terrorism.