WASHINGTON (REUTERS) - Analysis of a video showing American journalists James Foley and Steven Sotloff indicates that the video is authentic, a US National Security Council spokeswoman said.

"The US Intelligence Community has analysed the recently released video showing US citizens James Foley and Steven Sotloff," spokeswoman Caitlin Hayden said.

"We have reached the judgment that this video is authentic. We will continue to provide updates as they are available."

Islamic State militants posted a video purporting to show Foley being beheaded and also showing Sotloff.