Ankara, Nov 4 : Turkish authorities captured 40 undocumented migrants and detained a suspected human smuggler in a boat off the country's biggest city of Istanbul, local media reported. Turkish coast guard units launched an operation against illegal migration in the Black Sea off Istanbul's Sile district on the Asian side, Xinhua news agency quoted local media reports as saying. It added that the teams caught the migrants on a boat as they tried to sneak into Europe through the Black Sea. The migrants -- 24 Afghans, six Iraqis, five Iranians, two Syrians, and three Bangladeshis -- reportedly made a deal with a human smuggler to go to Europe via Turkey, according to Ihlas. Turkey, a key transit point for asylum seekers on their way to Europe, hosts more than 4 million refugees, including 3.7 million Syrians, within its borders, mostly in Istanbul. /IANS