"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," Obama said.
Five people died in the shooting at two military facilities in Tennessee, including suspected gunman Muhammad Youssef Abdulazeez. Three other people were injured.
In a statement, the FBI said it's investigating the shootings in conjunction with the Chattanooga Police Department and other law enforcement partners.
"As details of the investigation proceed, we'll make sure that the FBI as well as local law enforcement are providing the public with all the information that's involved," Obama said. "My main message right now is obviously the deepest sympathies of the American people to the four Marines that were killed."
Obama promised that the investigation would be prompt and thorough.
"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. And as we have more information, we'll let the public know."