Four Marines were killed and another injured after a gunman attacked two military facilities Thursday in Tennessee. The shooter was also killed.

Marine officials confirmed four Marine fatalities at the Navy and Marine Corps Reserve Center in Chattanooga in a statement on social media. The names of the Marines killed were not released, pending notification of the next of kin.

"Our priorities are focused on supporting the families of our Marines involved and assisting local investigators," the statement reads.

This April 2015 booking photo released by the Hamilton County Sheriffs Office shows a man identified as Mohammad Youssduf Adbulazeer after being detained for a driving offense. A U.S. official speaking on condition of anonymity identified the gunman in shootings at two Chattanooga military facilities as Muhammad Youssef Abdulazeez, who shares the same age and address as the man in the photo. (Hamilton County Sheriffs Office via AP)
This April 2015 booking photo released by the Hamilton County Sheriffs Office shows a man identified as Mohammad Youssduf Adbulazeer after being detained for a driving offense. A U.S. official speaking on condition of anonymity identified the gunman in shootings at two Chattanooga military facilities as Muhammad Youssef Abdulazeez, who shares the same age and address as the man in the photo. (Hamilton County Sheriffs Office via AP)

An April 2015 booking photo released by the Hamilton County Sheriffs Office shows a man identified as Mohammad Youssduf Adbulazeer.

Photo Credit: Hamilton County Sheriffs Office via AP

A sailor was also injured at the Reserve center, according to Navy officials, and a Marine recruiter, who worked at the Armed Forces recruiting center, sustained a wound to the leg. That Marine was treated at a local hospital and was released, according to Marine officials. The Associated Press reported that a soldier and police officer were also wounded in the attacks.

The gunman, who was identified by the AP as 24-year-old Muhammad Youssef Abdulazeez, from Hixson, Tennessee, first attacked the recruiting office, firing about 30 rounds into the glass doors and windows of the strip mall facility.

He then attacked the Reserve center at about 11 a.m., approximately seven miles away, according to Navy officials. There were multiple shots fired at that facility, which is used by Navy and Marine Corps personnel.

Marines and sailors there provide training and readiness support to Reserve personnel, in order to enable them to support the needs of the Navy and Marine Corps team, according to a statement from Navy officials. The Marine unit based there is Mike Battery, 3rd Battalion, 14th Marine Regiment — a Reserve artillery unit.

Navy and Marine officials continue to work with local and federal law enforcement as the investigation continues, according to the services.

In a Thursday afternoon press conference, Chattanooga Chief of Police Fred Fletcher said the attacker "brutally and brazenly attacked members of our armed forces."

U.S. Attorney Bill Killian added that the FBI was taking over the investigation.

"We are treating this as an act of domestic terrorism," he said.

When a defense official was asked Thursday about recent calls from members of the Islamic State group for attacks on service members, he said: "We did see an increase in chatter, but none of it was very specific." He was referring to intelligence reports/officials.

In a statement about the attacks, Navy Secretary Ray Mabus said military officials continue to do everything they can to keep troops and their family members safe.

"Though we can never fully prevent attacks like this, we will continue to investigate, review and guard against future vulnerabilities and do everything in our power to safeguard the security of our service members and their families," he said.

The glass window of the Armed Forces Career Center is riddled with bullet holes after a gunman opened fire on the building Thursday, July 16, 2015, in Chattanooga, Tenn. Authorities say there were multiple casualties including the gunman. (AP Photo/John Bazemore)
The glass window of the Armed Forces Career Center is riddled with bullet holes after a gunman opened fire on the building Thursday, July 16, 2015, in Chattanooga, Tenn. Authorities say there were multiple casualties including the gunman. (AP Photo/John Bazemore)

The glass window of the Armed Forces Career Center is riddled with bullet holes on July 16 after a gunman opened fire on the building in Chattanooga, Tenn.

Photo Credit: John Bazemore/AP

Mabus called the attacks devastating and senseless. He said the Navy and Marine Corps team collectively mourn the loss of four heroes, and offered his condolences to the families of those killed or wounded.

"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," Mabus said. "As the investigation unfolds, our priority will be to take care of the families of those affected."

Mabus also expressed his gratitude to those first to respond to the scene. He said their "prompt reaction was critical to stopping this individual from inflicting further violence."

Sen. Bob Corker, R-Tenn., chairman of the Senate Foreign Relations Committee who served as mayor of Chattanooga for four years until 2005, said he was heartbroken by the shootings that took place in his hometown.

"We have been in touch with federal, state and local officials and continue to monitor developments and have offered our assistance," he said in a statement. "This is a difficult day for Tennesseans and our thoughts and prayers are with all affected by this tragedy."

Staff writers Andrew Tilghman and Hope Hodge Seck contributed to this report.