Watch-list of suspected European Islamic State sympathisers stands at 10,000 people

Countries within the European Union have handed a list with the names of more than 10,000 suspected Islamic State sympathisers, she revealed.

This has created unmanageable pressure on immigration forces in Turkey.

Professor Jytte Klausen, who is the founder of the Western Jihadism Project, said the watchlist given to officials is a "capacity busting proposition".

"The Turks complained that they can't do it, and you know what, they can't," the Harvard and Brandeis University professor explained.

"It's a capacity busting proposition, to watch out for 10,000 westerners.

"They are not going to be able to check most names on that list of 10,000.

"Only if there is a case where there is an urgent bulletin out, because it has been discovered that they had left - and the urgent bulletin would be on the top of the desk - that's when you can catch people as happened here."

Her comments come hours after three British teenage boys were detained by officials in the country as they planned to travel to Syria.

The three teens were detained after British police were made aware on Friday two boys had gone missing and were believed to be travelling to Syria. 

Inquiries revealed they had travelled with a third person, the 19-year-old man.

It has been reported that the trio travelled to Spain and then took a flight to Turkey. 

Hayat Boumedienne, the widow of one of the terrorists who carried out an attack in Paris in January, also touched down in Syria via Turkey and Spain.

Prof Klausen described the indirect routes that are increasingly taken by would-be jihadists.

Due to gaps in intelligence sharing, travelling through another country makes it easier to arrive undetected.

She said: "There is not comprehensive data sharing among the European Union countries with respect to people who are merely suspected of doing something. Getting on a plane is subject to far less scrutiny than getting off a plane.

"Therefore you have airports like Gatwick, and other European airports, that have a lot of discount airlines flying out.

"They have been put under strict orders to look out for certain risk profiles. But they look out for their own folk, so at Gatwick, you are not going to look for people from Spain, and vice versa."

Booking seperate tickets and splitting up the journey to war torn Syria can make it more difficult for authorities to hunt down the would-be Jihadis, she warned.

She added: "It's become common practice to buy separate itineraries, so if you book on Ryanair to go to Spain, and you were booked on another itinerary to go from Spain to Istanbul, those two itineraries do not come up as connected travel documents when you leave Gatwick."

She added that Turkey was not the only route to reach Syria. "We do know of a number of people who have not flown directly from Spain to Turkey, but who have taken the far more cumbersome route through north Africa."

Once through immigration in Turkey, "It really is as easy as getting on a bus", she said.

"I think there is a lot of very innocent traffic there too (going to the border). 

"I have been on those buses in Turkey, everyone goes on the buses, there are a lot of tourists. How are you going to tell from a bunch of young girls who are tourists from people who want to go to Syria?"

She added: "These days most of them dress like tourists, or if they have a beard they shave it. The girls dress like normal teenagers."