Washington (CNN) - President Barack Obama on Thursday called the Fort Hood, Texas, shootings "tragic" and "a horrific outburst of violence."
He expressed his condolences for the shooting victims.
"These are men and women who have made the selfless and courageous decision to risk and at times give their lives to protect the rest of us on a daily basis," he said.
"It's difficult enough when we lose these brave Americans in battles overseas. It is horrifying that they should come under fire at an Army base on American soil."
Government authorities are working to ensure that Fort Hood is secure, he said. The president asked for all Americans to keep the soldiers from the base "in their prayers."
There is no greater honor or responsibility as president than making sure U.S. soldiers are properly cared for, he added.
"We will make sure that we get answers to every single question about this horrible incident," he pledged.
Twelve people died in the shooting - including a gunman - and about 30 were wounded, a Fort Hood spokesman told CNN.
Updated: 5:36 p.m.