Sgt.Anthony Sills, right, comforts his wife as they wait outside the Fort Hood Army Base near Killeen, Texas (AP)

A mass shooting at a military base in the US has left 12 people dead and dozens more injured, an army official has confirmed.

Lieutenant General Bob Cone, of Fort Hood in Texas, said a gunman open fired inside a station at which soldiers are readied for deployment to Afghanistan.

The killer, believed to be a member of the US army and named in reports as Major Malik Nadal Hasan, was shot dead at the scene. Two other suspects were arrested in relation to the incident were later released, but a fourth suspect was still in custody, army officials said.

The military base was placed on lockdown, with no vehicles allowed in or out of the compound.

Fort Hood is a sprawling 340 square mile military installation situated 50 miles south of Waco. It houses some 4,929 active duty officers and 45,414 enlisted members of the army.

Mr Obama said his thoughts and prayers were with the wounded and the families of the fallen.

He added: "It is 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."