Lt. Gen. Mark Milley told reporters Wednesday evening that the gunman had died from a self-inflicted gunshot wound.
Officials would not identify the alleged shooter until his family had been notified, but said that he served four months in Iraq in 2011 and had been undergoing treatment for depression and anxiety.
Milley also said that the alleged shooter had been "under diagnosis" for post-traumatic stress disorder but had not yet been officially diagnosed. He used a .45-caliber semi-automatic pistol purchased recently.
Read the full statement from Fort Hood officials here.
Officials at Scott & White Memorial Hospital said in a subsequent press conference that they were treating nine patients, three of whom were in critical condition. Other victims were transported to Carl R. Darnall Medical Center.
Wednesday's incident occurred less than five years after former U.S. Army psychiatrist Nidal Malik Hasan killed 13 people at Fort Hood.
Obama said in a statement that he was "heartbroken" that another shooting had taken place. He added that "we need to find out exactly what happened."
"I would hope that everyone across the country keep the families of Fort Hood in our thoughts and our prayers. The folks there have sacrificed so much on behalf of our freedom," he added.
Many of the people there have been on multiple tours of Iraq and Afghanistan, they served with valor, they served with distinction. At their home base they need to feel safe. We don’t yet know what happened tonight but obviously that sense of safety has been broken once again. We need to find out exactly what happened.
"There has been a shooting at Fort Hood and injuries are reported," Ford Hood said in an initial statement. "Emergency crews are on the scene. No further details are known at this time."
Fort Hood soldiers watching the news from Fort Irwin. pic.twitter.com/YYE9mv4oUn— Don Gomez (@dongomezjr) April 2, 2014
Army officials issued a 'shelter in place' warning on Twitter, but offered no additional details.
Instagram user fionashaytoon shared what appeared to be video of the shelter in place warning.