Turkey's coastguard closed the Dardanelles Straits to shipping on Thursday after launching a chase for a cargo ship carrying hundreds of illegal migrants.Despite the calls from the coastguard, including warning shots, the ship continued on its course. Security forces managed to board the vessel and captured some 400 illegal migrants, whose nationalities were not immediately made public.The authorities temporarily stopped the traffic on the busy Dardanelles Straits, a major international shipping route.Ahmet Çınar, the Mayor of Çanakkale province, said investigations are still ongoing into the cargo ship named 'Doğan Kartal'.Turkey has become a transit hub for refugees fleeing parts of the Middle East, North Africa and areas as far away as Afghanistan, hoping to reach Europe.Accidents involving ships illegally transporting the refugees and other migrants have cost dozens of lives.