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Obama: Marine deaths in Chattanooga shooting are "heartbreaking"

President Obama said Thursday that the deaths of four Marines who were shot by a lone gunman at a Chattanooga were "heartbreaking" and extended his sympathies to their families.

"It is a heartbreaking circumstance for these individuals who have served our country with great valor to be killed in this fashion. And although their families are still in the process of being contacted, I want them to know that I speak for the American people in expressing our deepest condolences and knowing that they have our full support as they try to overcome the grief that's involved here," the president said from the Oval Office, where he had just been briefed on the shooting by FBI Director James Comey.

Special Report: Five dead, including shooter, at military facility shootings

Earlier Thursday, a gunman opened fire at two military facilities in Chattanooga, Tennessee, killing at least four U.S. Marines and wounding a soldier and police officer. The shooter - who has been identified as Mohammod Youssuf Abdulazeez, sources told CBS News - was also killed.

The president also said of the local law enforcement officials who were injured, "we want them to know we are thinking of them."

"I'd ask all Americans to pray for the families who are grief stricken at this point and I want everybody to understand that we will be thorough and prompt in figuring out exactly what happened," he said.

U.S. Attorney Bill Killian said officials were treating the attacks as an "act of domestic terrorism." They are still investigating a motive, though, FBI Special Agent in Charge Ed Reinhold said. The first shooting happened around 10:45 a.m. and the attacks were over within a half-hour.

Shooter in Chattanooga attacks identified

After the shooting, the Department of Homeland Security said in a statement that it was "enhancing the security posture at certain federal facilities, out of an abundance of caution."

A U.S. official told CBS News that the shooter in Chattanooga was not on the radar of law enforcement for any possible terror links.

Defense Secretary Ash Carter also offered his thoughts and prayers and those of Defense Department officials to the families.

"The department will continue to work with local law enforcement as they investigate this heinous crime and will support our military families in their time of grief," he said.

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