WASHINGTON — Four Marines were killed Thursday in shootings at a pair of military facilities in Tennessee by a gunman who is being investigated for possible ties to Islamist terrorist groups, US law enforcement officials said.
The shooter, identified by the FBI as Mohammad Youssef Abdulazeez, 24, of Hixson, Tenn., was killed at the conclusion of a rampage that also left a Chattanooga police officer and a member of the US military wounded.
The assault marks the latest eruption of gun violence in the United States. It comes amid a flurry of recent arrests, disrupted plots, and warnings from US counterterrorism officials that the Islamic State has called on its followers to mount attacks against US targets, including military installations.
During brief remarks at the White House, President Obama described the Marines’ deaths as a ‘‘heartbreaking circumstance for these individuals who have served our country with great valor.’’
He avoided describing the attack as a terrorist plot, saying, ‘‘We don’t know yet all the details’’ and that ‘‘a full investigation is taking place.’’ Even so, Obama described stepped-up security measures as White House officials urged the Pentagon to ‘‘make sure that all our defense facilities are properly attentive and vigilant as we sort through what happened.’’
US officials said an initial check of federal terrorism databases produced no information that Abdulazeez had been under investigation.
The names of the Marines killed in the attack were not publicly disclosed Thursday as US military officials sought to reach members of their families. A military official, speaking on the condition of anonymity because he wasn’t authorized to discuss the case, said at least three of the Marines were from an artillery unit.
The Sixth Marine Corps Recruiting District, which includes Tennessee, has closed all facilities within 40 miles of the shooting as a security measure.
Ray Mabus, secretary of the Navy, said in a statement that ‘‘while we expect our sailors and Marines to go into harm’s way, and they do so without hesitation, an attack at home, in our community, is insidious and unfathomable.’’
Authorities said they had reached no conclusions about the shooter’s motivations. He had recently been arrested for driving under the influence and appears to have made frequent postings about his religious views online.
In one Internet posting this month, Abdulazeez had written ‘‘This life is a test of faith,’’ according to the SITE Intelligence Group, which monitors online postings by radical Islamist organizations and described the statement as an ‘‘aspiration for paradise.’’
Even so, friends who said they had been in recent contact with Abdulazeez said they saw no sign that he was violent.
Hussnain Javid, a student at the University of Tennessee at Chattanooga, said he was friendly with Abdulazeez and that they had both studied engineering.
Javid said that he ran into Abdulazeez about seven months ago at the Islamic Society of Greater Chattanooga and that Abdulazeez had recently moved back to the area and was looking for a job.
‘‘Everything seemed fine,’’ Javid said. ‘‘It is very shocking. He seemed to be a very nice young man.’’
The son of Kuwaiti and Palestinian parents, Abdulazeez was born in Kuwait but was a naturalized US citizen, according to the accounts of friends and relatives.
He grew up in the Chattanooga area, where he was on the wrestling team at Red Bank High School. Beneath what appears to be his senior photo in the school’s yearbook is a provocative quote: ‘‘My name causes national security alerts. What does yours do?’’
Public records indicate that he had no criminal history aside from vehicle-related offenses, including the April arrest.
He appears to have participated in mixed martial arts, and appears in a fight video on YouTube. An online résumé indicates that Abdulazeez had recently worked as a ‘‘procurement engineer’’ with Global Trade Express.
In a news conference in Chattanooga, Edward Reinhold, the special agent in charge for the FBI in Knoxville, declined to discuss details of the investigation, and would not say whether Abdulazeez had killed himself or was killed by law enforcement.
‘‘We will treat this as a terrorism investigation until it can be determined it was not,’’ he said. As news of the shooting spread, schools, a shopping mall, and roads in the area were all temporarily closed.
In the neighborhood where Abdulazeez lived, news footage late Thursday showed heavily armed law enforcement officers entering the family home and taking away at least one handcuffed woman in traditional Muslim garb.
Elijah Wilkerson has lived in the neighborhood only five years, but he says his wife often went walking with the Abdulazeezes.
‘‘It’s like a family down there,’’ Wilkerson said, gesturing to his street, currently blocked off by police. ‘‘I would have never imagined it would be up in here.’’
Dean McDaniel, 59, a longtime neighbor of the Abdulazeez family, said he regularly saw Abdulazeez and his siblings around the neighborhood.
The attack began at 10:45 a.m. when Abdulazeez fired rounds into the windows and door of a local military recruiting office. He then fled in a silver-colored Ford Mustang and drove to a Naval Reserve center several miles away, where he again opened fire and all five fatalities occurred.
Police in Chattanooga said shortly after 1:15 p.m. the shooting was over and the gunman was dead. Agents from the FBI and the Bureau of Alcohol, Tobacco, Firearms and Explosives converged on crime scenes littered with glass.
‘‘I know the whole rest of the state joins me in just a feeling of being sick in our stomach for the lives lost and the senselessness of this,’’ said Tennessee’s governor, Bill Haslam.
The attack came almost exactly a month after a shooting at a historically black church in Charleston, S.C., that prompted debate not only over the Confederate battle flag but also whether the terrorism label should be applied to the assault by a gunman allegedly motivated by racist views.
The shootings in Tennessee add to the mounting toll of US gun violence but are more likely to be seen as part of a growing danger attributed to the influence of the Islamic State and other terrorist groups.
FBI director James Comey recently disclosed that authorities had arrested more than 10 people over the past two months as part of a burst of activity by law enforcement to prevent attacks timed to the July 4 holiday and the Muslim observance of Ramadan.