U.S. authenticating video of American James Foley's execution

WASHINGTON -- Islamic State militants have released a video purporting to show the beheading of an American journalist, James Foley, as retribution for U.S. airstrikes in Iraq. The White House, his family and employer say they cannot determine the video's authenticity and are attempting to confirm whether he had been killed.

The 40-year-old freelance journalist from Rochester, New Hampshire, went missing nearly two years ago in northern Syria while on assignment for Agence France-Press and the Boston-based media company GlobalPost. He had not been heard from since.

At the end of the video, a militant shows a second man, who was identified as another American journalist, Steven Sotloff. The militant warns that Sotloff could be killed. Sotloff was kidnapped near the Syrian-Turkish border in August 2013 and freelanced for Time, the National Interest and MediaLine.

President Barack Obama has been briefed about the video on Air Force One as he returned to Martha's Vineyard, Massachusetts from Washington.

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 whether it is authentic.