Police said special operations teams conducted an operation in the Silivri district in the city's outskirts, detaining several people at a housing complex early on Thursday.
The sources did not provide an exact number for those rounded up, only saying that those detained came from China’s Turkic Uighur region of Xinjiang. They are suspected of "aiding and abetting" the gunman who, a top official said, was likely an Uighur.
On Wednesday, 27 people were arrested in a police operation in the western city of Izmir. The suspects were from Xinjiang, Russia's North Caucasus region of Dagestan, and neighboring Syria.
Turkish media have identified the gunman as a 28-year-old Kyrgyz man, who settled down together with his wife and two children in the Turkish province of Konya after arriving from Syria in November.
Deputy Prime Minister Numan Kurtulmus has suggested that "foreign intelligence services" could be behind the attack, which killed 39 people and wounded 65 others.
“I am of the opinion that it's not possible for the perpetrator to have carried out such an attack without any support. It seems like a secret service thing. All these things are being assessed,” he was quoted as saying on Thursday.
The pro-government Yeni Safak daily, citing security forces, reported on Thursday that attacker was believed to be hiding in a house in Istanbul, and security personnel were on a hunt for his hideout.
Turkish police forces have reportedly found documents belonging to the Daesh terrorist group in a number of houses raided in an effort to locate the assailant, Press TV reported.
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