Foley killing: What will the British government do?
20 August 2014 Last updated at 23:31 BST
David Cameron has described the killing of US journalist James Foley by an Islamic State militant as "shocking and depraved".
The prime minister has returned to Downing Street to hold meetings with the Foreign Secretary and senior intelligence officials.
The Metropolitan Police are investigating the contents of a video showing the killing and have warned the public that viewing, downloading or disseminating it might constitute an offence.
Nick Robinson reports.