By Tom Rayner, Middle East Reporter, on the Turkey-Syria border
A senior Turkish official has called on the international community to share more intelligence information to stem the flow of foreigners to Islamic State.
As the search continues for three London schoolgirls believed to be travelling to Syria, Cemalettin Hasimi told Sky News that Turkey cannot be expected to intercept people unless efforts are made to boost the country's travel blacklist.
"It's a global problem that requires a global response," said Mr Hasimi, who advises Turkish Prime Minister Ahmet Davutoglu on security and foreign policy.
"The only way to prevent their entrance is to know their name, to have a list, so that we can take necessary measures.
"It is a proven fact (that) the best way to prevent the mobility of these groups or individuals is in the source countries."
Turkey currently has a list consisting of around 10,000 individuals who will be detained and deported should they try to enter the country.
The list, compiled as a result of information shared by intelligence agencies around the world, has grown significantly in recent months.
It has grown from 5,000 names in the summer of 2014, to 7,000 names by the end of that year.
But as the case of the three missing London teenagers has shown, the task of identifying those who intend to travel to Syria remains difficult.
Although the Metropolitan Police spoke to the girls two months ago in connection with another student who travelled to Syria, that information was not passed to Turkish authorities.
Turkey attracts an average of 35 million visitors each year.
The country has established a network of Risk Analysis Centres at entry points, staffed by intelligence officials and expert profilers who assess travellers as they make their way into the country.
More than 500 people who were not on the travel blacklist have been detained and deported as a result of the checks over the past year.
They include a man from Norway carrying parts of an assault rifle in his luggage, and a Swedish citizen with bags of military-style camouflage and other equipment, who had travelled from Denmark.
Turkey is also stepping up its efforts along the Syria border, digging a trench nearly 60 miles long and three metres deep in the Kilis region.
It is also installing concrete walls to prevent vehicles, weapons and people being smuggled along the 600 miles of border it shares with Syria.
The governor of Kilis, Suleyman Tapsis, told Sky News authorities in the region have apprehended 184 foreigners from 34 different countries in the past year.
"We are catching them with military overalls, camouflage, binoculars and other such equipment," he said.
"They have computers and the photos we find on their USB sticks make clear they are in a troubled state of mind."
During a visit to Turkey in December, Prime Minister David Cameron insisted the UK was prepared to offer "the highest level of intelligence co-operation we can possibly achieve" with Turkey.
