Turkish police arrested around 50 foreign nationals in Istanbul early Sunday in a sweep targeting militants of ISIS group suspected of involvement in last weekend's Ankara suicide bombings, reports said.
The raid focused on several apartments in the Pendik suburb on Istanbul's Asian side, the NTV news channel reported.
It did not indicate the nationalities of those detained and questioned by police.
The Dogan news agency said the suspects were preparing to travel to Iraq and Syria to join ISIS.
Prime Minister Ahmet Davutoglu has said ISIS is the chief suspect in the double suicide bombing that killed 102 people at a peace rally in Ankara on October 10 in the deadliest attack in the country's modern history.
Turkish media reports have said one of the two bombers was identified as Yunus Emre Alagoz, brother of the man who carried out a similar attack in July in Suruc, a town in southern Turkey on the border with Syria, that killed 34 people.
The other, identified as Omer Deniz Dundar, had twice been to Syria in recent times, the reports said.
The attack has raised political tensions to new highs as Turkey prepares for a snap election on November 1, in a country that has become more polarised than ever.
Pressure has piled on President Recep Tayyip Erdogan, with opposition figures blaming him for security lapses over the Ankara attack.
For almost three months, Turkey has been waging an offensive against PKK militants, who have responded with attacks of their own, killing more than 140 members of the security forces.