Twelve people have been killed and 31 injured in a shooting at the Fort Hood¹ military base in Texas, the commander there has said.

美国德克萨斯州福特胡德军事基地发生枪击案，造成12人死亡，31人受伤。

US officials identified the shooter as Major Malik Nidal Hasan

Lt Gen Bob Cone² said the shooter had been killed in the incident and two suspects arrested. All were American soldiers. The base is locked down.

Lt Gen Cone said the motive³ for the shooting was not known. One of the dead was a policeman, others were soldiers.

President Barack Obama described it as "a horrific outburst（爆发，突发） of violence".

US media reports have named the gunman as Major Malik Nadal Hasan. He was reportedly in his late 30s or early 40s and due to be sent on a mission to Iraq.

Speaking at a press conference in Washington, President Obama said: "It is difficult enough when we lose these brave men and women abroad, but it is horrifying⁴ that they should come under fire at an army base on US soil."

He extended his condolences（吊唁，悼哀） to the families of the victims, adding: "We will make sure that we get answers to every single question about this horrible incident."

Mr Obama said the White House was working with the Pentagon, FBI and Department of Homeland Security to make sure Fort Hood was secure.

Fort Hood, near the town of Killeen, is the largest US base in the world.

Home to about 40,000 US troops, the base lies between Austin and Waco, about 60 miles (97 km) from each city.

Lt Gen Cone said the shooting had begun at about 1330 (1930 GMT) at a personnel and medical centre at Fort Hood, where soldiers who are preparing to deploy⁵（部署，配置） go for last-minute medical check-ups.

He said the shooter, who had two handguns, had opened fire and "due to the quick response of the police forces, was killed".

Two more suspects were apprehended⁶（逮捕，拘押） in an adjacent（临近的，毗邻的） facility, he said, adding that some eyewitness⁷ accounts suggested there might have been more than one shooter.

A serviceman stationed at Fort Hood who asked to remain anonymous⁸（匿名的） told the BBC: "I heard the emergency announcement over the speakers outside and saw people rushing to get indoors.

"In our office we're okay but we're hearing about the deaths. It's horrible and very shocking.

"We are still on lockdown（一级防范紧闭）. I am hearing that at least nine people may be dead. This is so terrible and frightening."

The BBC's Adam Brookes in Washington says units at Fort Hood are among those deployed⁹ in Iraq and Afghanistan, and some will have returned from there.

The base has a centre that deals with combat stress, our correspondent adds.

Hilary Shine, of the Killeen Fire Department told the BBC's News Channel Fort Hood was like a small city.

"It has schools, a hospital, a convenience store even. And it has a large daytime population - including civilians¹⁰ working on the base - with as many as 80,000 in this area during the daytime."

Local congressman¹¹ John Carter, speaking to NBC News, said gunfire had erupted（爆发） half an hour before a graduation ceremony was due to begin.

Texas Senator Kay Bailey Hutchison said in a statement: "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."