(CNN) -- A video released by ISIS shows the beheading of U.S. journalist James Foley and threatens the life of another American if President Barack Obama doesn't end military operations in Iraq.
In the video posted Tuesday on YouTube, Foley is seen kneeling next to a man dressed in black. Foley reads a message, presumably scripted by his captors, that his "real killer'' is America.
"I wish I had more time. I wish I could have the hope for freedom to see my family once again," he can be heard saying in the video.
He is then shown being beheaded. "We have seen a video that purports to be the murder of U.S. citizen James Foley by (ISIS)," National Security Council spokeswoman Caitlin Hayden said. "The intelligence community is working as quickly as possible to determine its authenticity. 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. We will provide more information when it is available."
Obama was briefed about the video, and "he will continue to receive regular updates," White House spokesman Eric Schultz said.
ISIS has carried out executions, including beheadings, as part of its effort to establish an Islamic caliphate that stretches from Syria into Iraq. In many cases, ISIS -- which refers to itself as the Islamic State -- has videotaped the executions and posted them online.
CNN is not airing the video.
Foley disappeared on November 22, 2012
, in northwest Syria, near the border with Turkey. He was reportedly forced into a vehicle by gunmen; he was not heard from again. At the time of his disappearance, he was working for the U.S.-based online news outlet GlobalPost.
On Tuesday, Foley's mother, Diane, took to social media with an emotional statement to praise and mourn her son.
"We have never been prouder of our son Jim. He gave his life trying to expose the world to the suffering of the Syrian people," she said in a post on the Free James Foley Facebook page
"We implore the kidnappers to spare the lives of the remaining hostages. Like Jim, they are innocents. They have no control over American government policy in Iraq, Syria or anywhere in the world.
"We thank Jim for all the joy he gave us. He was an extraordinary son, brother, journalist and person. Please respect our privacy in the days ahead as we mourn and cherish Jim.''