Last Updated Sep 29, 2015 7:30 AM EDT
TURKEY -- A report released Tuesday in the New York Times newspaper shows at least 30 thousand foreigners have joined ISIS (Islamic State of Iraq and Syria) since 2011. The fighters are from more than 100 countries, and more than 250 of them are American.
The road to the so-called Islamic State runs through Istanbul. Turkey's biggest city is just a bus ride away from the Syrian border through which those who wish to join ISIS are smuggled into the war zone.
Turkey has been accused of turning a blind eye to the thousands of foreign fighters crossing its border into Syria. However, CBS News correspondent Holly Williams reports that Turkish officials are cracking down, but they say it's impossible to stop the flow of Islamic extremists to groups like ISIS.
Turkey has a blacklist of 16,000 names, put together with the help of intelligence officials from the United States, Europe and other countries. If anyone on that list attempts to enter Turkey, he or she is stopped and deported. However, the blacklist is not enough, Williams reports, and foreign fighters are still slipping through the net.
Cemalettin Hasimi, a senior advisor to Turkey's prime minister, says that it is "definitely" impossible to catch everyone trying to make the trip from Turkey to Syria. Three teenage girls from Britain crossed into Syria in February, but a security video showing them in a Turkish bus station was only discovered after they had already joined ISIS.
Plain clothes Turkish police officers now have that bus station under 24 hour surveillance, and they are profiling travelers, Williams reports.
"From clothes style, from the way they're acting, from the way they're speaking, so it's quite a detailed process," Hasimi says.
Over 120 suspected foreign fighters have been caught at the bus station alone in the last five months, including several from North America, and Williams reports that in southern Turkey, another attempt is being made to stop Islamic extremists reaching ISIS territory: The Turkish government has begun building a concrete wall along part of its 500 mile long border with Syria.