President Obama called murder of four U.S. Marines in Chattanooga, Tenn., "heartbreaking" on Thursday, and said all of America is mourning their loss.

"My main message right now is, obviously, the deepest sympathies of the American people to the four Marines that have been killed," he said at the White House. "It is a heartbreaking circumstance for these individuals who have served our country with great valor to be killed in this fashion."

"And although the 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," he said.

Obama wouldn't name the suspect, but said one has been identified and that he seemed to act alone. The Federal Bureau of Investigation identified 24-year-old Muhammed Youssuf Abdulazeez, who was killed during the rampage, as the shooter.

Because the murders occurred at a Navy Reserve Center, Obama said that the White House has been in touch with the Pentagon to make sure that all defense facilities are being vigilant.

As for the law enforcement officers who responded to the two scenes, Obama said "we want to make sure that they know that we're thinking of them."

"We take all shootings very seriously," he continued. "Obviously, when you have an attack on a U.S. military facility, then we have to make sure that we have all the information necessary to make an assessment in terms of how this attack took place, and what further precautions we can take in the future."