The police found a hand-written note on one of the suspects detailing a migration route from Istanbul to Germany via Greece, Serbia and Hungary, including smuggler boats across the Mediterranean Sea, as well as several train and bus journeys.
The eight men told police that they were just tourists who had been planning to spend a few days in Istanbul and had booked rooms at a hotel, but no reservations were found under their names.
Turkey is the main launching point for migrants coming to Europe, and currently hosts over two million Syrian refugees.
More than 650,000 migrants and refugees, have reached the Greek islands so far in 2015 using the eastern Mediterranean route, the International Organisation for Migration (IOM) said earlier this month.
The Paris attacks however threw a security spotlight on the migrant flow, after the discovery at the scene of one of Friday`s attacks of a Syrian passport registered in the Greek island of Leros on October 3.
Turkey was long criticised by its Western allies for failure to take robust action to stem the flow of IS militants across its porous border.
But Ankara has stepped security measures in recent months after a series of deadly attacks blamed on the extremists, including a twin suicide bombing in Ankara that killed 102 people last month.
According to official data released to AFP last week, in the first half of 2015 over 700 foreign suspected jihadists were detained and deported from Turkey whereas for all of 2014 the figure was 520.
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