WASHINGTON: The United States said Wednesday that its special forces tried this summer to rescue American hostages held by Islamist militants in Syria.
News reports quoting government officials said Wednesday the captives included James Foley, the American journalist whose graphic execution by an Islamic State jihadist was revealed in a video Tuesday.
Foley was kidnapped in northern Syria in November 2012 and his grisly murder has provoked revulsion and condemnation.
The Pentagon confirmed the failed hostage-rescue operation but did not specify whether Foley was among the captives.
"This operation involved air and ground components and was focused on a particular captor network within ISIL (IS)," Pentagon spokesman Rear Admiral John Kirby said in a statement, referring to the Islamic State.
"Unfortunately, the mission was not successful because the hostages were not present at the targeted location."
The White House said in a statement that President Barack Obama "authorized action at this time because it was the national security team's assessment that these hostages were in danger with each passing day in ISIL (IS) custody."
In the execution video, a black-clad militant said that Foley, a 40-year-old freelance journalist, was killed to avenge US air strikes against his movement.
The man then paraded a second US reporter, Steven Sotloff, before the camera and said he too would die unless Obama changes course.
In the nearly five-minute video, 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.
'Cancer' of extremism
Obama demanded Wednesday the world take action against the "cancer" of jihadist extremism in Iraq. The Islamic State has seized much of eastern Syria and northern Iraq.
As US jets continued to strike IS targets in Iraq, despite the threat hanging over Sotloff, Obama said: "When people harm Americans anywhere, we do what's necessary to see that justice is done."
Shortly after he spoke, the State Department asked for 300 more US troops to be sent to Iraq to protect US facilities.
Obama paid tribute to Foley and said the Islamic State must be defeated.
"Jim Foley's life stands in stark contrast to his killers," he said, branding the militants genocidal murderers who target civilians and subject women and children to "torture and rape and slavery.
"We will be vigilant and we will be relentless... From governments and peoples across the Middle East, there has to be a common effort to extract this cancer so it does not spread."
US intelligence believes the video is genuine, and the British government held a crisis meeting to launch an investigation because Foley's executioner spoke English with a London accent.
"We have not identified the individual responsible, but from what we have seen, it looks increasingly likely that it is a British citizen," Prime Minister David Cameron told reporters. "This is deeply shocking."
'Jim wouldn't want us to hate'
Foley's parents, John and Diane, appeared on the lawn of their home in New Hampshire to pay tribute to their son -- the oldest of five adult children -- and call for other hostages to be released.
"Jim would never want us to hate or be bitter. We cannot do that and we are just so very proud of Jimmy and we are praying for the strength to love like he did," Diane said.
US Central Command said 14 air strikes had been carried out on IS targets in Iraq in the 24 hours since the video was released.
The United Nations and Europe's top powers have condemned the killing.
French President Francois Hollande said Thursday he was "outraged" at the execution of Foley by Islamic State jihadists, accusing them of barbarism.
The head of the international police organisation Interpol, Ronald Noble, condemned the beheading of Foley and called for a global response to the threat posed by Islamic extremists.
In a significant shift from its usual policy, Germany said it was ready to send weapons to support Iraqi Kurds against IS.
In June, the group then known as the Islamic State in Iraq and the Levant declared the dawn of a Muslim caliphate and seized control of a swath of eastern Syria and northern Iraq.
This month, Obama reacted by ordering US warplanes to counter threats to US personnel in the Kurdish regional capital Arbil or to civilian refugees from Iraqi religious minority groups.
He has insisted the scope of the strikes would remain limited, but Iraqi officials and observers have argued that only foreign intervention could turn the tide on jihadist expansion in Iraq.
Shiite militias, federal soldiers, Kurdish troops and Sunni Arab tribes have been battling IS for weeks in some areas but have been unable to clinch a decisive victory. (AFP)