SAN ANTONIO ? (UPDATE 2) At least 12 people were killed at Fort Hood military base in Texas on Thursday, including one gunman, the facility's commander said.
Lieutenant General Robert Cone said the killing spree began at around 1:30 p.m. local time, when at least one soldier opened fire on fellow troops at the base, one of the world's largest military facilities.
"At this time, we are looking at 12 dead and 31 wounded," Cone said in a statement broadcast on CNN.
The toll included one gunman, but Cone said more suspected shooters were later caught.
"We since then have apprehended two additional soldiers who are suspects."
"They tracked the suspected individuals to an adjacent facility, and they were apprehended. They are soldiers, but they are suspects at this time, and we are looking at that."
Both gunmen were wearing military uniform, but it was not immediately clear if they were soldiers or in disguise, Texas Senator Kay Bailey Hutchison said.
It was too early to determine a motive for the attack on the biggest US military base in the world in Killeen, in central Texas, a spokesman for Homeland Security added.
President Barack Obama had been informed of the shooting and was to give a statement, White House officials said, as staff in the situation room monitored the unfolding drama.
"Department of Emergency Services confirmed at approximately 1:30 p.m. November 5 that more than one shooter fired shots into the Soldiers Readiness Processing Center and Hoowze Theater on Fort Hood," a statement from the base said.
"Emergency personnel have responded to the scene and evacuated several wounded."
The shooting erupted first in the theater where a graduation ceremony for local schools was being held, a Pentagon official said.
Gunfire then broke out in the soldier processing center at the base which has up to 29,000 troops and civilians most of whom have completed extensive tours of duty in Iraq and Afghanistan.
Base spokesman Sergeant Major Jamie Poston told CNN television the military was "not sure right now" what had happened.
"At this point we're looking for the other shooter.... Emergency services responded. Have evacuated a number of wounded," he added.
"We are on the lookout for the second shooter," Poston said.
A Killeen police department spokeswoman warned there were still suspects at large. "All the suspects are not in custody at this time," she told AFP. "I know they have active shooters out there."
MSNBC reported speculation of a third gunman. One of the shooters at large was believed to have a high-powered sniper rifle, and was holed up in a building surrounded by SWAT teams, MSNBC said.
Senator Hutchison said that up to 30 people had been wounded and told CNN that two of the gunmen were wearing military uniform, but it remained unclear whether they were soldiers.
"I am shocked and saddened by today?s outburst of violence at Fort Hood that has cost seven of our brave service members their lives and has gravely injured others. My heart goes out to their loved ones," she added in a statement.
Local congressman John Carter said the gunfire had erupted ahead of a graduation ceremony when one of his aides was warned of gunfire.
"A soldier came running up to him saying, "sir, don't go over there. They are ? somebody is shooting over there," Carter told MSNBC.
?When the soldier ran by him, he saw the soldier didn't know it, but he was wounded. So, he went into the building and they stopped him, because he had been shot.?
Fort Hood has been working to rehabilitate many soldiers suffering from post-traumatic stress syndrome, Carter added.
A message on Fort Hood's website ? the headquarters of the Army 3rd Corps, the 4th Infantry Division and the 1st Cavalry Division ? said it was closed due to an emergency. All those units have seen extensive duty in Iraq.