Washington: The United States admitted Thursday that the Islamic State is the most dangerous group it has faced in recent years and warned that the Middle East faces a long-term battle to defeat it.
Pentagon chiefs said the jihadist group could be eradicated if local Sunni communities reject it and regional powers unite to fight it, but only if the battle is taken into Syria and not just Iraq.
Speaking after the US military said it had already carried out a failed hostage rescue mission inside Syria, and against the backdrop of new air strikes in Iraq, they warned IS poses a considerable threat.
"They marry ideology and a sophistication of strategic and tactical military prowess," Defense Secretary Chuch Hagel said. "They are tremendously well funded. This is beyond anything we have seen."
General Martin Dempsey, chairman of the Joint Chiefs of Staff, said: "This is an organization that has an apocalyptic end of days strategic vision that will eventually have to be defeated."
Dempsey warned the jihadist vision of a wider Muslim caliphate could "fundamentally alter the face of the Middle East and create a security environment that would certainly threaten us in many ways."
"Can they be defeated without addressing that part of the organization that resides in Syria? The answer is no," he said, when asked if the campaign against the group could go beyond Iraq.
He said the fight could not be won by US military prowess alone but only with regional support and that of "the 20 million disenfranchised Sunni that happen to reside between Damascus and Baghdad."
Washington has launched air strikes against IS positions and boosted arms supplies to Kurdish forces, but still wants Baghdad`s Shiite-led government to open its arms to Sunni moderates.
The warning came after the IS on Tuesday released a video showing a militant with a British accent beheading American journalist James Foley, and threatening a second US hostage.
The murder has stoked fears in Britain and beyond that the territory the militants have seized in Syria and northern Iraq could become a launching pad for a new round of global terror attacks.In six bombings near a dam north of Mosul, US warplanes damaged three Humvee armored trucks, another vehicle and several roadside bomb "emplacements," according to US Central Command.
The US military said it has conducted 90 air strikes in Iraq since August 8, including the latest raids. Fifty-seven of those operations were to support of Iraqi government forces near the Mosul dam.
Separately, officials confirmed that in recent months, US special forces carried out a raid inside Syria to try to rescue people held hostage by IS militants, reportedly including Foley.
"This operation involved air and ground components and was focused on a particular captor network," Pentagon spokesman Rear Admiral John Kirby said.
"Unfortunately, the mission was not successful because the hostages were not present at the targeted location."
Foley, a 40 year-old freelance journalist, was kidnapped in northern Syria in November 2012. His employer GlobalPost said his captors had demanded a 100-million-euro ($132 million) ransom.
GlobalPost CEO Philip Balboni said his team had never taken the demand seriously, and State Department deputy spokeswoman Marie Harf insisted bluntly that: "We do not pay ransoms."
She said the United States estimates that IS militants have already received millions of dollars worth of ransoms so far this year alone. Most are believed to have been paid by European governments.
In the execution video, released online, a black-clad militant said that Foley was killed to avenge US air strikes against IS.
The man, speaking with a clear London accent, then paraded a second US reporter, Steven Sotloff, before the camera and said he would die unless Obama changes course.
Sotloff is a freelance journalist for Time magazine. His family has asked for privacy, and asked friends and neighbors to avoid speaking to the press, Miami`s CBS 4 television reported.
Frank Castle, the boyfriend of Sotloff`s sister, said on his Facebook page that the journalist was captured on August 4, 2013, "and up to this point it has been under wraps due to a media blackout."US Attorney General Eric Holder said that the FBI already had opened a criminal probe into Foley`s kidnap.
"We have long memories and our reach is very wide," Holder said. "We will not forget what happened and people will be held accountable -- one way or the other."
The scale of the threat became clear in June when the group, then known as the Islamic State in Iraq and the Levant, declared the dawn of a caliphate and seized the Iraqi city of Mosul.
Obama reacted this month by ordering US warplanes to counter threats to US personnel in the Kurdish regional capital Arbil and to civilian refugees from Iraqi religious minority groups.