FBI special agent Ed Reinhold says the Navel reserve shooting in Chattanooga, Tenn., which left five people dead, including the shooter, will be treated as a "terrorism investigation until we determine it was not." (WTVC News Channel 9)

The gunman who opened fire at a Naval facility in Tennessee on Thursday morning, killing four Marines, has been identified as Mohammod Youssuf Abdulazeez, according to the FBI.

Authorities say they are investigating the shooting as a possible terror attack. Before he was killed Thursday afternoon, Abdulazeez, 24, also wounded a member of the Navy, a Chattanooga police officer and a third person, military officials said.

“It is a heartbreaking circumstance for these individuals who have served our country with great valor to be killed in this fashion,” President Obama said during remarks delivered from the Oval Office.

He said he wanted the families of the victims to know “they have our full support as they try to overcome the grief that’s involved here.”

Obama said that he has been in touch with the Pentagon and said officials were working to make sure other defense facilities were well protected.

“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,” Ray Mabus, secretary of the Navy, said in a statement.

Abdulazeez, of Hixson, Tenn., opened fire at the Navy Operational Support Center, which the U.S. Navy said provides support for reserve component personnel, after he shot at an armed forces recruiting center.

An April 2015 booking photo released by the Hamilton County Sheriff’s Office showing the suspected gunman. (Hamilton County Sheriffs Office via AP)

The Pentagon said Thursday afternoon that the four Marines would be identified after next of kin were notified.

“Somebody brutally and brazenly attacked members of our armed services,” Fred Fletcher, the Chattanooga police chief, said at at a news conference.

Edward Reinhold, the special agent in charge for the FBI in Knoxville, declined to discuss details of the investigation, which he described as in its initial stages. He would not say if Abdulazeez killed himself or was killed by law enforcement.

“We will treat this as a terrorism investigation until it can be determined that it was not,” he said. However, Reinhold later added: “We have not determined if it was an act of terrorism or a criminal act.”

The FBI’s Knoxville field office is investigating the shooting along with the Chattanooga Police Department and other law enforcement agencies.

Reinhold said that the shooting appeared to be the work of a lone gunman, and said Abdulazeez did not work at either facility. He had “numerous weapons” on him during the shooting, Reinhold said, and was not wearing body armor.

The shooting is being treated as “an act of domestic terrorism,” U.S. Attorney William C. Killian said. However, Killian said that the investigation would bear out precisely what kind of crime this was, and he cautioned people not to get caught up in the label.

Reinhold said there was no intelligence suggesting that an attack was coming on Thursday. A senior FBI official said the shooting did not initially appear to be related to any international terrorist group.

President Obama asked that the nation pray for the families of the victims in the shootings at a Naval facility in Chattanooga, Tenn., which left five people dead including the shooter. (AP)

Abdulazeez had writte two posts recently writing that “life is a test of faith,” according to the SITE Intelligence Group, which monitors online postings by radical Islamist organizations. In one post, he also emphasized the importance of making sacrifices in the name of Islam.

Hussnain Javid, a student at the University of Tennessee at Chattanooga, said he was friendly with Abdulazeez. They both studied engineering. Abdulazeez’s resume said that he graduated in 2012 with a degree in electrical engineering.

Javid ran into Abdulazeez about seven months ago at the Islamic Society of Greater Chattanooga, and he said Abdulazeez had 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.”

According to court records, Abdulazeez was charged with driving under the influence in April.

The family “didn’t bring much attention to themselves,” said Dean McDaniel, 59, a longtime neighbor of the the Abdulazeezes. He said Mohammed’s younger sister regularly babysat for McDaniel when his children were younger and that he regularly saw all three kids around the neighborhood.

“He was a good kid,” McDaniel said. “I trusted him in my home.”

McDaniel said he was “stunned” when he heard news of the shooting and said nothing he ever noticed in Mohammed’s behavior would have led him to predict this.

As the gunshots rang out in southeastern Tennessee, police and federal authorities scrambled in response to an active shooter situation that locked down schools and closed roads throughout the area.

“This is…a nightmare for the city of Chattanooga,” Mayor Andy Berke said at a news conference.

The shootings began at 10:45 a.m. and ended within 30 minutes, Reinhold said. He said that the gunman opened fire at one facility before driving to another, where he continued to shoot.

Police in Chattanooga said shortly after 1:15 p.m. that the active shooter situation was over, and they later confirmed that the gunman was dead, though they did not say whether he was killed by police or by his own hand.

“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,” Gov. Bill Haslam (R) said earlier in the day.

The armed forces recruiting center houses members of all of the services, said Kelli Bland, a spokeswoman for the U.S. Army Recruiting Command in Fort Knox.

“According to our personnel on the ground, our recruiting center was not hit with any of the shots,” Bland said in a telephone interview.

(WRCB-TV via AP)

There was initially confusion regarding where the gunfire erupted and what had happened.

The Navy had initially said there was no shooting at a reserve center on Amnicola Highway in Chattanooga, before tweeting a short time later that it had confirmed a shooting at an unspecified building on Amnicola Highway. Navy officials had also said they were investigating a shooting at the recruiting building.

Special agents from the Bureau of Alcohol, Tobacco, Firearms and Explosives responded to the shooting.

President Obama was briefed on the shooting by his national security staff, White House spokesman Eric Schultz said Thursday afternoon.

“I am heartbroken by the tragic shootings that have taken place today in my hometown,” U.S. Sen. Bob Corker (R-Tenn.), who served as Chattanooga’s mayor before he was elected to the Senate, said in a statement. “We have been in touch with federal, state and local officials and continue to monitor developments and have offered our assistance. This is a difficult day for Tennesseans and our thoughts and prayers are with all affected by this tragedy.”

Due to the shooting, officials locked down a shopping mall, schools and other buildings Thursday.

Chattanooga State Community College said that due to a shooting near the campus, the school’s main campus was placed on lockdown. The lockdown was later lifted and the school said it was closing for the remainder of the day. Lee University, a Christian school in nearby Cleveland, Tenn., was also locked down, as was the Chattanooga Health Department.

Meanwhile, the Bradley Square Mall in Cleveland was closed after someone reported hearing shots fired there. In a post on Facebook, the mall said that there were no shots fired there, but said the added security was “based on an incident in Chattanooga.” The mall later closed to allow police to conduct a search and said it would reopen at 5 p.m.

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Authorities in other areas also vowed to increase security. The New York City Police Department placed additional officers at military recruiting stations in the city, according to John J. Miller, the department’s deputy commissioner for intelligence and counterterrorism.

Erica Wright, who works at a salon near the recruiting center, told CNN that she heard “one pop, a really loud pop.” She then rushed to the salon door and heard “several other pops after that.”

The shooter was firing from a convertible car, Wright said, and opened fire at “the naval recruiting place” before driving away.

Brian Murphy contributed to this report.

[This post was first published at 12:15 p.m. It has been updated and will continue to be updated.]