Damascus: The apparent beheading by extremists of a US journalist sparked worldwide revulsion on Wednesday and drew pledges by outraged Western governments to aid those battling the militants.
In a video posted online Tuesday, a masked militant is shown beheading a man resembling James Foley, who has been missing since he was seized in Syria in November 2012.
The video also contains a threat from the Islamic State (IS) extremist group to kill another reporter if US air strikes in Iraq continue.
The release of the video comes as the US air raids appear to have yielded some results, helping Kurdish and federal forces push IS fighters back from some recently-conquered areas in northern Iraq, including the strategic Mosul dam.
Europe's top powers swiftly condemned the extremists, with France warning the world faced the "most serious international situation" since 2001.
British Prime Minister David Cameron cut short his holiday and rushed back to London, calling an urgent meeting to discuss how to deal with IS after the man filmed carrying out the apparent beheading had a British accent, prompting speculation he is a UK national.
In a highly significant move, Germany said it was ready to send weapons to support Iraqi Kurds in their battle against IS, while France vowed to hold a conference on the security of the region and the battle against the "barbaric" militants.
Rights group Amnesty International said the apparent execution-style killing was a "war crime".
The White House said US intelligence was studying the video, and that President Barack Obama had been briefed on it as he flew from Washington to resume his vacation at Martha's Vineyard.
"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," National Security Council spokeswoman Caitlin Hayden said.
Foley was an experienced correspondent who had covered the war in Libya before heading to Syria to follow the revolt against Bashar Al Assad's regime, contributing to news site GlobalPost, Agence France-Presse (AFP) and other media outlets.
AFP chairman Emmanuel Hoog described Foley "as a brave, independent and impartial journalist" whose work in Syria and other war zones was "widely admired". According to witnesses, Foley was seized in the northern Syrian province of Idlib on November 22, 2012.
A message to America
In the nearly five-minute video, titled "A Message to America," IS declares that Foley was killed because Obama ordered air strikes against IS in northern Iraq.
The beheading is carried out in an open desert area with no immediate signs as to whether it is in Iraq or Syria by a black-clad masked militant who speaks in English.
Foley is seen kneeling on the ground, dressed in an orange outfit that resembles those worn by prisoners held at the US naval base at Guantanamo Bay.
"Any aggression towards the Islamic State is an aggression towards Muslims from all walks of life who have accepted the Islamic caliphate as their leadership," the masked militant declares.
He threatens to kill another man shown in the video and said to be Steven Sotloff, whose kidnapping in August 2013 has not been widely reported. He has written for several US newspapers and magazines, including Time, Foreign Policy and The Christian Science Monitor.
UN aid for Iraqis
Meanwhile, the UN refugee agency said it had launched a huge operation on Wednesday to bring desperately needed aid to half a million Iraqis.
"It's the largest single aid push we have mounted in more than a decade," UNHCR chief Antonio Guterres said in a statement.
The first Boeing 747 of the 10-day operation flew into the Iraqi Kurdish city of Arbil from Jordan carrying 100 tonnes of aid including tents, plastic sheets, kitchen sets, and