According to Reuters, Islamic State (IS) militants posted a video on Tuesday (March 19) that purported to show the beheading of US journalist James Foley in retaliation for US air strikes against the insurgents in Iraq.
The video, entitled "A Message To America," also reveals images of another US journalist, Steven Sotloff, whose life in IS said is dependent on how the United States acts in Iraq.
The gruesome video presented President Barack Obama with bleak options that could define America’s involvement in Iraq and the public reaction to it, potentially dragging him further into a conflict he built much of his presidency on ending.
Obama held back from making a public statement about the beheading until the video could be formally authenticated.
"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," White House National Security Council spokeswoman Caitlin Hayden said in a statement.
Other political leaders were swift to react.
British Prime Minister David Cameron interrupted his holiday to return to London to lead the hunt to identify the apparent executioner speaking with a British accent who killed Foley.
Foreign Secretary Philip Hammond said he was not surprised to hear the British accent and that large numbers of Britons were fighting in Iraq and Syria.
"Our intelligence services will be looking very carefully on both sides of the Atlantic at this video to establish its authenticity, to try to identify the individual concerned and then we will work together to try to locate him," Hammond told SKY NEWS.
French President Francois Hollande called for an international conference to discuss how to strike back at IS.
Iraqi Foreign Minister Hoshiyar Zebari urged the world to back his country against IS, which he described as a threat to the world, not just to the minority ethnic groups whose members it has killed in Iraq.
Germany and Italy both offered to send arms to bolster the military capabilities of Iraqi Kurds fighting IS in northern Iraq.
COMMENT: The video's grisly message was unambiguous, warning of greater retaliation to come against Americans following nearly two weeks of US air strikes that have pounded militant positions and halted the advance of the militants, which until this month had captured a third of Iraq with little resistance.
Foley, 40, was kidnapped by armed men on November 22, 2012, in northern Syria while on his way to the Turkish border, according to GLOBALPOST, a Boston-based online publication where Foley had worked as a freelancer. He had reported in the Middle East for five years and had been kidnapped and released in Libya.
Sotloff, who appeared at the end of the video, went missing in northern Syria while reporting in July 2013. He has written for TIME among other news organizations.
On Facebook, Foley's mother Diane Foley said: "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. "We implore the kidnappers to spare the lives of the remaining hostages. Like Jim, they are innocent. They have no control over US government policy in Iraq, Syria or anywhere in the world."
IS, which has declared a caliphate in the parts of Iraq and Syria it controls, opened the video with a clip of Obama saying he had authorized strikes in Iraq.
A man identified as James Foley, his head shaven and dressed in an orange outfit similar to uniforms worn by prisoners at the US military detention camp in Guantánamo, Cuba, is seen kneeling in the desert next to a man standing, holding a knife and clad head to toe in black.
"I call on my friends, family and loved ones to rise up against my real killers, the US government, for what will happen to me is only a result of their complacency and criminality," the kneeling man says.
The man next to him, in a black mask, speaks in a British accent and says, "This is James Wright Foley, an American citizen, of your country. As a government, you have been at the forefront of the aggression toward IS."
Following his statement he beheads the kneeling man. At the end of the video, words on the side of the screen say, "Steven Joel Sotloff", as another prisoner in an orange jumpsuit is shown on screen. "The life of this American citizen, Obama, depends on your next decision," the masked man says.
University of Virginia political scholar Larry Sabato said the current situation was more like the beheading of American journalist Daniel Pearl by al-Qaeda leader Khalid Sheikh Mohammed in 2002. He said it could help bolster a growing perception among Americans that the United States will have to be more aggressive in dealing with IS militants.
Syria has been the most dangerous country for journalists for more than two years. At least 69 other journalists have been killed covering the conflict there and more than 80 journalists have been kidnapped in Syria.
The US-based Committee to Protect Journalists estimates that approximately 20 journalists are currently missing in Syria. Many of them are believed to be held by IS.
Islamic State also released a video on Tuesday that gave a strong indication it might try to strike American targets. The video with the theme of "breaking of the American cross" boasts Islamic State will emerge victorious over "crusader" America.
It followed a video posted on Monday, warning of attacks on American targets if Washington strikes against its fighters in Iraq and Syria.
As well as taking one-third of Iraqi soil, IS has seized a number of oil wells in northern Iraq. The government in Baghdad said it was troubled by reports that IS was smuggling oil to export markets and warned the purchase of such supplies could help the group fund its operations.