European ISIS fighters: Are there really 3,000 jihadis?

How big is the homegrown ISIS threat?

The European Union’s Anti-Terrorism Chief Gilles de Kerchove told the BBC Friday that the number of Islamic State fighters from Europe is "probably above 3.000, which is unprecedented."

That statement prompted a number of sensational headlines - especially in Britain, where the Parliament voted Friday to join the airstrikes against ISIS.

But 3,000 Islamic State fighters is probably an inflated figure. Mr. de Kerchove himself qualifies that total saying 3,000 includes all those who have been to the region, including those who have returned and those who have been killed there.

The European jihadis threat assessment includes the dead? Out of those estimated 3,000, how many of those European ISIS jihadis are still alive?

If Europeans are trying to assess the long-term risk of the ISIS campaign becoming a domestic terror threat, this is a relevant number. And what's the breakdown on those IS fighters who are already back in Europe vs. those still in the Middle East?

In the US, the ISIS threat suddenly got smaller this week.

Last week,  Matthew Olsen, the director of the National Counterterrorism Center, said: "Thousands of foreign fighters have flocked to Syria over the past three years. This includes more than 2,000 Europeans and more than a hundred Americans."

The figure of more than 100 Americans fighting with ISIS has been cited by several Obama administration officials and members of the US Congress.

But on Thursday, the FBI director challenged that number.

 The US only knows of about 12 Americans who are currently in Syria fighting, FBI Director James Comey said Thursday.

Where did the "more than 100 Americans" fighting with IS figure come from?

"When I use a number of more than 100, that means people who have gone and come back, people who have attempted to go and we locked them up, people who have gone and stayed," Mr. Comey said during an interview with reporters at FBI headquarters, according to the Associated Press.

That sounds very similar to how the Europeans are counting ISIS fighters.

As The Christian Science Monitor reported earlier this month, most political leaders are over-exaggerating the Islamic State domestic terrorism threat.

The most cited research out there comes from a study conducted by a Norwegian expert of extremism, Thomas Hegghammer, between 1990 and 2010. His research showed that only one of nine foreign fighters who had come home were motivated to carry out an attack.

It’s a figure that officials don’t necessarily accept as fact, but it does provide a baseline for them to assess threats. In an interview with The Christian Science Monitor, for a cover story on European jihadis, the European Union’s counterterrorism coordinator Gilles de Kerchove says that even if the threat is “one percent of more than 2,000 [jihadis], that is 20 very dangerous guys" who’ve been trained, indoctrinated, and woven into networks across the Sunni world. “Their level of tolerance for violence will have increased significantly,” says Mr. De Kerchove.

Note that a little more than a month ago, de Kerchove said the European IS fighter tally was "more than 2,000."

The International Center for the Study of Radicalization at King’s College London, also estimated a month ago that as many as 2,000 Europeans have already fled to Syria. The French government estimates 700 young people have left from France alone – the largest number from any country on the Continent. Up to 500 youths from Britain have joined Syrian rebel groups, more than 300 from Germany, and at least 100 from the Netherlands, the Monitor reported, in its story "Why young Europeans are becoming jihadis."

When asked by the BBC by the sudden jump in his estimate of European jihadis, de Kerchove said: "It's steady growth. I wouldn't say it's a 'boom.' And probably the statement of the establishment of a caliphate played a role. If you believe in this, probably you want to be a part of it as early as possible and not to arrive late."