Secretary of Defense Chuck Hagel said Wednesday that the problem of 'foreign fighters' aiding the self-proclaimed Islamic State of Iraq and al-Sham (ISIS) includes far more Americans than has been previously reported – at least 100 and counting.

'We have acknowledged publicly we are aware of over 100 U.S. citizens who have U.S. passports who are fighting in the Middle East with ISIL forces,' he said during a televised interview.

'There may be more. We don't know.'

Earlier estimates had only about a dozen so-called 'foreign fighters' from the United States scattered across the Middle East in ISIS army units.

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Chuck Hagel said more than 100 Americans are fighting in the Middle East alongside ISIS militants, a dramatic uptick from previous estimates of about a dozen

Foreign fighter: Abdirahmaan Muhumed, pictured in Syria, was killed while fighting for ISIS. He had access to planes at Minneapolis-St. Paul International Airport before he joined the Islamist terror group

A few have been killed on the battlefield, including 29-year-old Somali-American Abdirahmaan Muhumed, was employed cleaning jetliners for Delta Airlines before he left the U.S. to fight for the terror group.

Another, Douglas McArthur McCain, was killed in Syria weeks ago. It emerged later that he was a close friend of another foreign fighter, Troy Kastigar, who was killed in 2009 after joining the al-Shabab terror network in Somalia.

All three hailed from the Minneapolis, Minnesota area, in an area with a concentrated Muslim population and at least one mosque tied to radical anti-American ideology.

The New York Times reported six days ago that according to American intelligence and law enforcement agencies, 'nearly a dozen Americans' had traveled to Syria to fight for ISIS.

The Economist magazine put the number at 70 on Tuesday, citing a mishmash of statistics from the International Monetary Fund, the London-based International Centre for the Study of Radicalisation and Political Violence, and the New York-based Soufan Group.

But hard numbers have been hard to come by, and Hagel's admission sheds new light on the size of the problem.



U.S. officials have warned that Americans who could use their passports to bring the ISIS fight back home pose one of the greatest homeland security threats to the United States since the 9/11 al-Qaeda attacks in 2001.

Speaking Tuesday at the White House, Obama's chief spokesman said that the U.S. officials 'have been focused on countering the threat' for months.

'The Department of State in March appointed Ambassador Robert Bradtke as senior adviser for partner engagement on Syria foreign fighters,' White House Press Secretary Josh Earnest told reporters.

'So there’s been an intensive diplomatic effort to coordinate our efforts to confront and mitigate this threat. There’s been significant operational collaboration between DHS, FBI and all of their foreign counterparts, including Interpol, on this effort.

President Obama drew criticism Wednesday in Estonia for backing off of his resolve to 'destroy' ISIS with a weaker pledge to make it 'manageable'

Douglas McArthur McCain (left), who died fighting for ISIS in Syria this year, was a high school pal of Troy Kastigar (right), who died fighting for al-Shabab in Somalia in 2009

Hagel said Wednesday that with so many American passport-holders able to re-enter the U.S. after joining the ISIS jihad, 'we can't take a chance ... on saying, "Well, let's technically define this. Is it a real threat today or tomorrow?"'

He reiterated the resolve of U.S. officials including President Barack Obama and Secretary of State John Kerry to wipe the Islamist terror group off the map.

America's mission in Iraq, Hagel said on CNN, is 'not "contain." It’s exactly what the president said: "degrade and destroy".'

Obama caught flak on Wednesday morning in Estonia for waffling between hard-line and soft-pedal positions on the Islamist group that has cut a wide and deadly swath through massive portions of eastern Syria and northern Iraq.

The primary U.S. objective 'is to degrade and destroy' ISIS 'so that it’s no longer a threat not just to Iraq but also the region and to the United States,' the president said during a press conference.

But minutes later he said a successful American effort in the region would 'shrink' the group's 'sphere of influence, its effectiveness, its financing, its military capabilities to the point where it is a manageable problem.'

Obama arrived at RAF Fairford in Gloucestershire, England on Wednesday ahead of a NATO summit



The president was greeted by an American entourage led by U.S. Ambassador to the UK Matthew Barzun

Missouri Republican Sen. Roy Blunt was among the lawmakers who lashed out later in the day.

'Terrorists who behead Americans are not "manageable," Blunt said in a statement. 'They must be stopped, and we need President Obama to communicate a clear strategy and goals on how he plans to eliminate this threat.'

Hagel, meanwhile, clung to Obama's first statement while ignoring the second.

'You've got to destroy it,' he said of ISIS, 'because if we don't destroy it, it will get worse.'

The soft-spoken defense secretary stopped short of offering any guarantees, however.

'Vows are something beyond my mortal capacity of doing,' he said. 'We will do everything possible that we can do to destroy their capacity to inflict harm on our people and Western values and our interests.'

The Pentagon will achieve the White House's strategic objectives, Hagel explained, by cooking up a menu of tactical options for Obama to choose from.



Steven Sotloff (left) was beheaded in a gruesome video distributed by ISIS this week, following a heart-rending videotaped appeal to the terror group's leaders last week from his mother (right)

'Our mission,' he said, 'is to provide him those options and those plans to accomplish the mission of "destroy and degrade" the capability of ISIS.'

And speaking of the growing number of Americans who have taken up arms against U.S. interests and allies in the Middle East, he conceded that 'this crowd is a dangerous crowd.'

'This crowd is as dangerous a group of people – beyond just terrorists – they are an army,' he said, 'marrying this with an ideology and a capacity to do things.'

'They control half of Iraq today. They control half of Syria today. We better be taking them seriously.'

Obama will lead a UN Security Council meeting this month devoted to the question of how to handle foreign fighters and whether to restrict their movements.

British Prime Minister David Cameron has called for new anti-terrorism powers to limit their access to the UK and determine where they can and can't go.

Kerry said earlier in the day that American might would pursue the killers of two American journalists whose beheadings were captured on video and spread globally through social media.