The White House said it has not confirmed the authenticity of a video that purports to show the killing of American journalist James Foley by Islamic State group militants.
White House National Security Council spokeswoman Caitlin Hayden said the administration has seen the video and that the intelligence community is working as quickly as possible to determine if it is authentic.
“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,” she said in a statement.
Mr Foley, a freelance journalist, went missing in Syria nearly two years ago.
The release of the video allegedly showing his death comes amid a US airstrike campaign against Islamic State group targets in Iraq.
The group has declared an Islamic state in the territory it controls in Iraq and neighbouring Syria, imposing its harsh interpretation of Islamic law.