WASHINGTON (REUTERS) - The White House said on Tuesday that US intelligence agents were working to verify the authenticity of a video purported to show the murder of an American journalist by Islamic State and expressed outrage if it turns out to be genuine.

"We have seen a video that purports to be the murder of US citizen James Foley by ISIL. The intelligence community is working as quickly as possible to determine its authenticity," White House spokesman Caitlin Hayden said. "If genuine, we are appalled by the brutal murder of an innocent American journalist and we express our deepest condolences to his family and friends."