Police arrested as many as seven alleged Islamic State members Tuesday during raids on various addresses in Istanbul, Turkish news agencies said.
The reports said police acted on information gathered in part by German intelligence, and that attacks on German targets in Istanbul might have been planned.
Also Tuesday, Turkish security forces stopped 10 suspected IS terrorists who were apparently trying to sneak into the country from Syria.
One of the suspects was wearing a suicide vest that police said was ready to explode.
Turkey is on edge after being hit by four suicide bombings since the start of the year. Officials blame IS or Kurdish militants for the attacks.
Three Israeli citizens and an Iranian were killed in the latest attack, which occurred Saturday when a suicide bomber blew himself up along Istanbul's main shopping street.