A British woman living in Hong Kong was one those who was killed in the bomb attack in Bangkok that killed at least 22 people.
Foreign Secretary Philip Hammond confirmed the Briton, who has not yet been named, is among those killed in the bomb blast at the Erawan Shrine that also left more than 120 people injured.
He said: "The loss of life and injury in Bangkok is horrific and I condemn this callous act of violence against completely innocent and unsuspecting members of the public. I can confirm that one British national, a resident of Hong Kong, lost her life in the attack. British Embassy staff in Thailand are assisting her family at this very difficult time. My thoughts are with the victims, their families and loved ones, and with the Thai people."
Prime Minister David Cameron added: "[I am] Deeply saddened to hear a British national was killed in the horrific Bangkok bombing. My thoughts are with her family & all those affected."
The Foreign Office said it is in contact with the Thai authorities and has offered UK assistance with the investigation. British nationals in Thailand are also being advised to check the Foreign Office website for the latest travel advice.
At least nine others killed in the attack in the Thailand capital are believed to be from China, Hong Kong, Malaysia, Singapore and the Philippines. Nobody has claimed credit for the attack and a motive is not yet clear. CCTV footage of a suspect wearing a yellow T-shirt and carrying a backpack has emerged during the hunt for the attacker.
Prime Minister Prayuth Chan-ocha said the man seen in the footage is believed to be from an "anti-government group based in Thailand's north east".
In a separate attack, an explosive device was thrown at a pier in Bangkok. No one was injured during the second incident as the device bounced into the water before detonating.