ISIS has released a video that shows the beheading of U.S. journalist James Foley.
The video also shows the group threatening the life of another American if President Barack Obama doesn't end military operations in Iraq.
The National Security Council confirmed the authenticity of the video on Wednesday.
In the video posted Tuesday on YouTube, Foley is seen kneeling next to a man dressed in black. He 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," Foley can be heard saying in the video.
He is then shown being beheaded.
Obama was briefed about the video and "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.
Foley disappeared Nov. 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.''
The video also shows another American journalist. In the video, the militant, who speaks English in what sounds to be a British accent, claims the journalist's life is dependent upon what Obama does next.
That journalist is believed to be Miami native and University of Central Florida graduate Steven Sotloff, who was kidnapped at the Syria-Turkey border in 2013. Sotloff is a contributor to Time and Foreign Policy magazines.
On Wednesday, Pinecrest police were spotted outside Sotloff's family's home, as his family members did not want to speak with reporters who were stationed outside.
U.S. Rep. Illeana Ros-Lehtinen has been in contact with Sotloff's family since his capture. On Wednesday, she told Local 10 News "We never had proof of life. Unfortunately now we see this video. What a horrific organization this ISIS is. They have no respect for human life."
On Wednesday we also heard from Sotloff's former roommate at UCF. "Yesterday was the first time his dad had seen or heard from his son since December, and of course that’s not the circumstances you want to hear or see him in," said Emerson Lotzia. "His dad wasn’t in the worst spirits yesterday because as of right now he knows his son is alive. He hadn’t known since December if his son was alive or not."
The Committee to Protect Journalists estimates there are about 20 journalists missing in Syria, many of them held by ISIS.
Among them is American Austin Tice, a freelance journalist who was contributing articles to The Washington Post. Tice disappeared in Syria in August 2012. There has been no word of from him since his abduction.
As a freelancer, Foley picked up work for a number of major media outlets, including Agence France-Presse and GlobalPost.
"On behalf of John and Diane Foley, and also GlobalPost, we deeply appreciate all of the messages of sympathy and support that have poured in since the news of Jim's possible execution first broke," Philip Balboni, GlobalPost CEO and co-founder, said in a published statement, referring to James Foley's parents.
"We ask for your prayers for Jim and his family."
Foley had previously been taken captive in Libya. He was detained there in April 2011 along with three other reporters and released six weeks later.
Afterward, he said that what saddened him most was knowing that he was causing his family to worry.
Foley grew up in New Hampshire and graduated from Northwestern University's Medill School of Journalism in 2008. Like other young journalists who came of age after the September 11 terror attacks and American wars overseas, Foley was drawn to Iraq, Afghanistan and other areas of conflict.
Friends described Foley as fair, curious and impressively even-tempered.
"Everybody, everywhere, takes a liking to Jim as soon as they meet him," journalist Clare Morgana Gillis wrote in a blog post about him in May 2013, six months after he disappeared in Syria.
"Men like him for his good humor and tendency to address everyone as 'bro' or 'homie' or 'dude' after the first handshake. Women like him for his broad smile, broad shoulders, and because, well, women just like him."
The video of Foley was released as ISIS is being targeted by American airstrikes ordered by Obama.
"I think they may have been surprised and are doing the best they can to retaliate," former CIA director R. James Woolsey, Jr. told CNN.
Foley's killing recalled the murder of Daniel Pearl, The Wall Street Journal correspondent who was kidnapped while reporting in Pakistan in January 2002. His murder was captured on video and posted on line by al Qaeda.
It also harkened to the videotaped beheadings of Americans Nicholas Berg, Eugene Armstrong and Jack Hensley carried out by al Qaeda during the height of the Iraq War.
Pentagon Press Secretary Rear Adm. John Kirby released the following statement late Wednesday afternoon:
"The United States attempted a rescue operation recently to free a number of American hostages held in Syria by the Islamic State of Iraq and the Levant (ISIL). This operation involved air and ground components and was focused on a particular captor network within ISIL. Unfortunately, the mission was not successful because the hostages were not present at the targeted location.
"As we have said repeatedly, the United States government is committed to the safety and well-being of its citizens, particularly those suffering in captivity. In this case, we put the best of the United States military in harms' way to try and bring our citizens home.
"The United States government uses the full breadth of our military, intelligence and diplomatic capabilities to bring people home whenever we can. The United States will not tolerate the abduction of our people, and will work tirelessly to secure the safety of our citizens and to hold their captors accountable."