One very nasty night I had two 737s inbound EDDH. Initially 15 minutes apart they ended up in formation over, then, East Germany. There was one gap and they ewere both going for it. I could only gave them traffic info, when requested, and let them get on with it.
Air Defence told me to tell them to turn back. Passing the message on only resulted in me being told wherethey could put their SAMs.
Made an entry in the log in case it resulted in an international incident however common sense prevailed and I never heard anything more