The FBI is leading a national security investigation, U.S. Attorney General Loretta Lynch said in a statement. Witnesses said they heard scores of shots.

The Marine Corps flag hanging from Nathan Bill’s Restaurant on Island Pond Road in Springfield.

CNN reports the shooting suspect was armed with an AK-47 style weapon and carrying 30-round magazines at the time of the attack according to two law enforcement officials briefed on the investigation. Names of those slain were not released.

“The senseless violence that occurred in Tennessee is a awful tragedy made worse by the fact that the fearless individuals whose lives were taken answered the call to serve and protect our nation”. They are hard to stop because the extremists aren’t directed by the terror groups, US officials say. The 24-year-old suspect, who was also killed, was born in Kuwait and became a naturalized USA citizen.

Abdulazeez was a 2012 graduate of the University of Tennessee in Chattanooga, where he earned a degree in electrical engineering, the university said.

He added Muslims should not miss an opportunity to “submit to Allah”.

He was arrested by Chattanooga police April 20 on a DUI charge.

But a woman who attended Red Bank High School with Abdulazeez told the Chattanooga Times Free Press that he was a quiet kid and well-liked. “I’ve never had any kind of conflict with them”. “But to lose four in Chattanooga, Tennessee, is just heartbreaking”, she told reporters.

Eyewitnesses reported seeing the gunman firing from inside a auto outside the recruitment centre.

The two entrances to the fenced facility have unmanned gates and concrete barriers that require approaching cars to slow down to drive around them. It is the responsibility of the Department of Defense to disclose the identities of the Marines. He said investigators had “no idea” what motivated the shooter, but “we are looking at every possible avenue, whether it was terrorism, whether it’s domestic, international, or whether it was a simple criminal act”.

The gunman then drove off to a Naval Reserve Center about 6 miles (10 km) away, fatally shooting the four Marines before being shot and killed in a firefight with police.

Earlier, U.S. officials said authorities were investigating whether the gunman was inspired by or had links to the Islamic State (IS) group or other jihadist organisations.

The Federal Bureau of Investigation (FBI) identified the shooter as Mohammod Youssuf Abdulazeez, who was also killed in a firefight with the police.

Four Marines were killed and three others were injured in the hail of gunfire, which authorities say began at a military recruiting center in the strip mall, then continued at a nearby military installation. Ramadan ends Friday.

Those who knew him have spoken of their shock at hearing of his involvement. “We monitor to see what force posture to take”.

Plastic cups mark evidence outside the Armed Forces Career Center after a gunman open fire on the building Thursday, July 16, 2015, in Chattanooga, Tenn. Chattanooga Mayor Andy Berke said there’s “an officer down” at a military reserve center.

Chattanooga is a city of about 173,000 people along the Tennessee River in the southeast of the state.