Attacks by Islamist militants pose the biggest security threat for Germany and events like the shooting and bombing in Istanbul this week could happen in Germany, the head of the country's domestic intelligence agency (BfV) told a Saturday newspaper.

Three suspected Islamic State suicide bombers killed 44 people at Istanbul's main airport on Tuesday, the deadliest in a string of attacks in Turkey this year.

"We can't rule out attacks like those in Istanbul also happening in our country," Hans-Georg Maassen told German newspaper Frankfurter Allgemeine Zeitung.

He said recent military defeats for Islamic State were not demoralising jihadists here, and attacks in Europe were becoming ever more important for Islamic State to intimidate people and send the message to followers that "we're still here".-Reuters