A video reportedly showing the execution of an American journalist who was kidnapped on Thanksgiving in 2012 was analyzed and confirmed by the U.S. government Tuesday morning.

PBS reported that James Wright Foley, who was a freelancer and contributed to NBC and Global Post along with PBS, was killed by ISIS -- based on a video that was originally posted on YouTube.

Foley's mother appeared to confirm the news of her son's death Tuesday, on Facebook, and said she had never been prouder of him, Huffington Post reports.

"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.

President Barack Obama addressed the public from Martha's Vineyard Wednesday after the video's authenticity was confirmed.

"The entire world is appalled," Obama said, according to ABC.

The video begins with a clip of Obama at a press conference, followed by Foley kneeling in an orange outfit next to a man dressed in all black, with his face covered, holding a gun.

Foley appears to read aloud a script telling viewers that America is his real killer and that he wishes he had more time to see his family.

The man in black then speaks, in what sounds like a British accent, and warns America that ISIS has been accepted by many and they are now a fully organized army.

He then appears to begin to behead Foley, at which point the video blacks out and reopens to a Foley lying on his stomach, with his head placed on his back.

"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," National Security Council spokeswoman Caitlin Hayden told Fox.

At the end of the clip, another American is shown on the screen in the same kneeling position as Foley was. The militant speaks directly to Obama and says any further attacks will result in a similar fate for another journalist, Steven Joel Sotloff.

Foley's mother, in her Facebook post, said, "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. "

U.K. Prime Minister David Cameron returned immediately to London, cutting short his summer vacation, after seeing the video, according to NBC.

British Foreign Secretary Philip Hammond told NBC the video appears to be genuine.

"We are very concerned by the apparent fact that the murderer in question is British," Hammond told NBC News partner ITV News. "We are urgently investigating."

The British accent of the militant in the video confirms the concerns of the government, and Cameron has recently said there are at least 400 nationals in ISIS, NBC reported.

Obama is expected to make an announcement regarding the video Wednesday.