The U.S President Barack Obama has said the entire nation is grieving after a shooting that killed 13 people at a Texas army base. He said he had ordered all flags at the White House and other Federal buildings to be flown at half mast until Veterans Day on 11 November.<br/><br/>Major Nidal Malik Hasan, 39, a US-born Muslim and army psychiatrist, opened fire at Fort Hood on Thursday. According to military official sources, Mr. Hasan was due to be deployed soon to Afghanistan. Family members said Mr Hasan was strongly opposed to the deployment and had wanted to leave the army.<br/><br/>Mr Obama cautioned against jumping to conclusions and said the motives for the shooting are being investigated.<br/><br/>Mr Hasan was shot four times during the attack and is currently being treated in hospital under armed guard.<br/>