US President Barack Obama has said the beheading of US journalist James Foley is “an act of violence that shocks the conscience of the entire world”.
Mr Obama said the ideology of Islamic State, the group which made a video of Mr Foley's killing, was “bankrupt” and would ultimately fail.
IS said Mr Foley's death was revenge for US air strikes on its fighters in Iraq, according to the BBC.
The UN, UK and others have expressed abhorrence at the video.
Mr Foley's mother Diane said he "”gave his life trying to expose the world to the suffering of the Syrian people”.
Mr Foley, 40, had reported extensively across the Middle East, working for US publication GlobalPost and other media outlets including French news agency AFP.