President Barack Obama is promising a prompt investigation into the attacks that left five people - including four Marines and the sole gunman - dead at two separate military centers in Chattanooga, Tennessee.

Speaking from the Oval Office moments ago, Obama called the shooting a "heartbreaking circumstance."

"My main message right now is obviously, the deepest sympathies to the American people," Obama stated. "To the four Marines that have been killed, it has been a heartbreaking circumstance for these individuals who have served our country with great valor to be killed in this fashion."

He said that all of the details are not yet known, but a full investigation is taking place.

The FBI is taking the lead and will work closely with the local law enforcement agencies.

Obama also said that he has been in touch with the Defense Department to make sure military facilities are vigilant. 

The president just returned to Washington from a trip to Oklahoma. 

(See full updates, here.)

Watch Obama's remarks in the video above.

UPDATES: 4 Marines Killed in Attacks on 2 Chattanooga Military Centers

Chattanooga Shooter Identified as Muhammad Youssef Abdulazeez