A video claiming to show the beheading of the kidnapped journalist Steven Sotloff has been uploaded to a file-sharing site.
American authorities are trying to verify the video, with the state department saying it is "sickened" by the news.
Two weeks ago, the jihadi group Islamic State (also known as Isis) released a video showing the beheading of photojournalist James Foley. Steven Sotloff appeared in that recording alive. Both recordings appear to show the same killer, who spoke with a British accent.
David Cameron has called the beheading "absolutely disgusting and despicable".
Sotloff was kidnapped last year, having previously worked in Libya, Bahrain and Egypt.