British Prime Minister David Cameron is to chair a meeting of the government’s emergency response committee on Sunday to discuss an ISIS video showing the beheading of British aid worker David Haines.
Cameron, who returned to London ahead of schedule on Saturday night, had called the murder an act of pure evil and vowed to bring the aid worker’s killers to justice.
“This is a despicable and appalling murder of an innocent aid worker. It is an act of pure evil. My heart goes out to the family of David Haines who have shown extraordinary courage and fortitude throughout this ordeal,” he said in a statement.
“We will do everything in our power to hunt down these murderers and ensure they face justice, however long it takes.”
Haines is the third Westerner beheaded in recent weeks by the ISIS, the first two were U.S. journalists.
British officials kept news of Haines’ abduction out of the public eye for security reasons until ISIS showed him in a video nearly two weeks ago.
U.S. President Barack Obama said after the killing that the United States would stand with Britain in an expanded effort against the terror group.