James Foley was "aware of the dangers" but "believed in what he was doing", a friend has said, after video appearing to show the journalist's death was released.
Film-maker Matthew VanDyke told BBC Radio 4's Today programme seeing news of his friend's apparent execution was "a complete nightmare"
"He was certainly aware of the dangers, he was very professional," he said.
"He had a love for what he did and he wanted to tell the story of the Syrian people. And nothing was going to stop him from doing that."
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.