Four people, including the gun man, have been killed and dozens reportedly injured in the shooting incident, media reports said. "We're following it closely," said Obama at a Chicago restaurant.
Obama also said the situation is "fluid" right now, and his national security team is in close contact with not just the Defense Department, but also the Federal Bureau of Investigation (FBI), according to the White House.
"I want to just assure all of us that we are going to get to the bottom of exactly what happened," Obama said.
"Obviously this reopens the pain of what happened at Fort Hood five years ago," Obama said of another shooting rampage in 2009, which left 13 people dead and more than 30 wounded.
Law enforcement officials said the shooting so far has left at least four dead and more than a dozen injured, Xinhua reported.