Turkish police detained 38 people, some of them Syrian citizens, over suspected links to ISIS in an operation on Thursday in the northwestern province of Bursa, the state-run Anadolu news agency said.
Counter-terrorism police carried out simultaneous raids on homes in various districts of Bursa, smashing doors open with battering rams and searching the properties, it said.
ISIS militants have carried out gun and bomb attacks in Turkey. Many foreign fighters passed through Turkey in recent years on their way to join the jihadist group in territory it controlled in Syria and Iraq.
A year ago, the group claimed responsibility for a New Year's Day mass shooting by a lone gunman who killed 39 people in a packed Istanbul nightclub. A trial of those allegedly behind the attack began this month.