Pentagon calls Islamic State threat 'beyond anything we've seen'

US Defense Secretary said on Thursday that Islamic State militants could possibly pose an even bigger threat to the United States than Al-Qaeda, and pledged efforts to weaken the group would continue.

Speaking at a press conference at the Pentagon, Hagel also said that potential airstrikes in Syria are on the table, and defended the unsuccessful attempt by American Special Forces to rescue murdered photojournalist James Foley and other Western hostages.

"[Islamic State militants] are an imminent threat to every interest we have, whether it's in Iraq or anywhere else,” he said, as quoted by Reuters.

Responding to a question on whether or not the extremists are a threat on the scale of Al-Qaeda, which carried out the September 11, 2001 attacks on the World Trade Center, Hagel noted that "ISIL is as sophisticated and well-funded as any group that we have seen."

"They're beyond just a terrorist group. They marry ideology, a sophistication of strategic and tactical military prowess. They are tremendously well-funded. Oh, this is beyond anything that we've seen. So we must prepare for everything," he added.

The comments come in the wake of a graphic video released by Islamic State earlier this week, which showed a masked, English-speaking man beheading Foley and threatening to murder another one if President Barack Obama did not halt his renewed airstrike campaign in Iraq. The individual is thought to be British born, and a member of a trio of hostage caretakers known by the group as ‘The Beatles,’ in reference to their shared UK nationality.

The militant Sunni group IS represents an extreme take on Islam, and began increasing its strength as civil war raged through Syria over the last three years. When the group initiated its campaign in Iraq, it was able to quickly take over territory in the western and northern parts of the country, in part thanks to the toleration of Sunni communities disaffected with the Shia-led government in Baghdad.

Its brutal tactics began making headlines around the world as it targeted religious and ethnic minorities, threatening them with death if they did not convert to their own brand of Islam. When militants forced tens of thousands of people up a mountain in order to avoid death, the US reacted by renewing humanitarian and military action in Iraq. At the press conference Thursday, Hagel said this effort has been effective so far.

"American air strikes and American arms and assistance helped Iraqi and Kurdish forces blunt ISIL's advance around Arbil, where American diplomats and troops are working, and help the Iraqis retake and hold-Mosul dam," he said.

At the same time, however, General Martin Dempsey, the chairman of the US Joint Chiefs of Staff, cautioned that the Islamic State could not be defeated without international efforts aimed at its base in Syria.

"This is an organization that has an apocalyptic, end-of-days strategic vision that will eventually have to be defeated," he said, according to the Huffington Post. "Can they be defeated without addressing that part of the organization that resides in Syria? The answer is no."

Meanwhile, the Global Post published the letter sent by IS to Foley’s family about one week before his death. In the letter, the group called its hostages “the scum of [US] society,” and said it would execute Foley “as a direct result” of American “transgressions” in Iraq.

The letter states that the Foley family was given “many chances to negotiate” his release, but the Post disputed this statement, saying the journalist was missing for more than a year before IS even made its initial contact with the family. After demanding about $132 million, it did not send another message until August 12, just one day before the video of Foley’s murder was released.

As RT reported previously, US and UK intelligence agencies are working on identifying Foley’s killer, with British Prime Minister David Cameron already admitting on Thursday that the individual seen in the video appeared to be British. One of the IS member’s former hostages claimed his name was “John,” saying he is a key negotiator for the militants and is “intelligent, educated and a devout believer in radical Islamic teachings.”