Turkish counter-terror police detained 40 foreign nationals in raids in Istanbul over their suspected links with Islamic State, Turkey's state-run Anatoly news agency reported on Sunday.
Police carried out simultaneous raids to 23 addresses in Istanbul's conservative Faith district detaining suspects from Afghanistan, Iran, Iraq and Azerbaijan, Anatoly said.
Some suspects are identified as having gone to the conflict areas inside Syria several times, Anatoly said.
Turkey has suffered a series of suicide bombings and attacks by Islamic State and Kurdish militants over the past year. It launched its first major military incursion into Syria last month to push jihadists away from its border and prevent Kurdish fighters from seizing territory as they retreated.
Thousands of foreign fighters from countries including Turkey, Britain, Europe and the United States have joined the Islamist militants in their self-proclaimed caliphate in recent years, many of them passing through Turkey.
Ankara has since launched a crackdown on the networks facilitating their passage.
At least seven suspected suicide bombings across Turkey since July 2015, which have killed more than 250 people, have been blamed on Islamic State.
A network of suspected Turkish Islamic State militants is responsible for at least two of the attacks, Turkish prosecutors have said in legal documents, while foreign members of the group were accused of being behind the suicide bombing at Istanbul Ataturk airport in June.