David Cameron is returning to Downing Street this morning to hold meetings over the "shocking and depraved" murder of journalist James Foley, No 10 said.
In graphic footage released by the Islamic State, Foley is apparently beheaded by a militant who speaks with a British accent.
"If true, the brutal murder of James Foley is shocking and depraved," a No 10 statement said.
"The Prime Minister is returning to Downing St this morning. He will meet with the Foreign Secretary and senior officials from the Home Office, Foreign Office and the agencies to discuss the situation in Iraq and Syria and the threat posed by ISIL terrorists."
A British family have told ITV News of their devastation after discovering a close relative is fighting with the Islamic State in Iraq.
A French journalist who was held hostage with James Foley in Syria has told ITV News it was "devastating" to see his murder.