Prime Minister Gordon Brown has sent a message of condolence and support to US President Barack Obama after an Army psychiatrist killed 13 soldiers in a gun rampage at a Texas army base.
Mr Obama described the attack at Fort Hood, carried out by American-born Muslim Major Nidal Malik Hasan, as an "horrific outburst of violence".
In his message to the president Mr Brown said: "My thoughts are with the families and friends of those killed or injured and with you as you find the strength and words to help America respond."
Armed with two non-military issue pistols, including a semi-automatic, Hasan, a military psychiatrist, entered a section used to prepare soldiers for deployment overseas and started firing.
Within minutes, 13 soldiers at the base were dead or dying in the worst mass shooting yet at a military base in the US.
At least 30 others - including two civilians - were injured. Officials were trying to establish the motive behind the attack.
Tory leader David Cameron also expressed his "shock" in a letter to President Obama.
"My heart goes out to the families and friends of those who have been killed and injured in this terrible incident," he wrote.
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"It is especially distressing these personnel should have lost their lives while preparing to leave the safety of home and protect the United States and her allies in danger zones overseas.
"Coming so soon after the deaths of five British soldiers in a single incident in Afghanistan earlier this week, it is another tragic reminder of how much both of our countries owe to our men and women in uniform."
