PARIS • When the bodies of Islamic State in Iraq and Syria (ISIS) fighters are recovered on the Syrian battlefield, the passports found on them have often been stamped in Turkey, which thousands of recruits pass through on their way to join the terror group.
Fighters who call relatives abroad often do so using Turkish cellphone numbers, and when they need cash, they head to Western Union offices in southern Turkey, according to court and intelligence documents.
From the start of ISIS' rise through the chaos of the Syrian war, Turkey has played a central, if complicated, role in the group's story. For years, it served as a rear base, transit hub and shopping bazaar for ISIS, and at first that may have protected Turkey from the violence the group has inflicted elsewhere.
Now, the Turkish government and Western officials say the suicide bombings at Istanbul's main airport on Tuesday bore the hallmarks of an ISIS attack, and they have added them to a growing roll call of assaults attributed to the group in Turkey in recent months.
Analysts said Turkey was paying the price for intensifying its action against ISIS. Under international pressure, the country began sealing its border last year, as well as arresting and deporting suspected militants. And last summer, Turkey allowed the United States to use Incirlik Air Base to fly sorties over the group's territory in Syria and Iraq.
"Turkey has been cracking down on some of the transit of foreign fighters who are flowing into as well as out of Turkey, and they are... allowing their territory to be used by coalition aircraft," CIA director John O. Brennan told Yahoo News recently.
"So there are a lot of reasons why Daesh would want to strike back." Daesh is the Arabic acronym for ISIS.
The centrality of Turkey for foreign volunteers flocking to ISIS is evident in court documents and intelligence records. As so many of the group's foreign fighters passed through Istanbul's Ataturk Airport, the destination itself became synonymous with the intent to join ISIS. Dozens of young men and women were arrested by the FBI in the US and by officials in Western Europe after they booked flights to Istanbul.
When ISIS fighters communicated with worried family members, it was often with Turkish SIM cards. And investigation records show that two fighters who were arrested in Austria late last year, and who the police believed were supposed to take part in the Paris attacks on Nov 13, had been sent money from their ISIS handler through a Western Union office in Turkey.
Mr Bulent Aliriza, director of the Turkey Project at the Centre for Strategic and International Studies, said Turkey had not been quick enough to recognise the threat ISIS would pose. "Where Turkey can be accused of negligence is failing to understand... that these radicals... would morph into an organisation that not only threatened the West, but ultimately itself," he said.
NEW YORK TIMES