(Take this with a grain of salt, some of it has been reported by tabloids. What we can assume as fact from photos is that the plane is in Cologne and has been evacuated via slides).
There's an official statement from the police in Cologne here:
POL-K: 170610-1-K Verkehrsmaschine landet außerplanmäßig in Köln-Bonn - Verdächtige Flugpassagiere festgenommen | Pressemitteilung Polizei Köln
Basically confirming that passengers alerted cabin crew to conversations with "terroristic content" between 3 men. Captain decided to land in CGN, aircraft evacuated via slides in secured area, 3 men arrested, backpack connected to them examined by bomb disposal personnel who performed a controlled detonation. Backpack (or what remains of it) still being examined, aircraft has been searched with dogs, suspects being interrogated, investigation ongoing.