There is a method interrupTalking in FliteController. However there is a comment in the header file before this method.
// Handling not doing voice recognition on Flite speech, do not directly call
It looks like its just calling [AvAudioPlayer stop] and setting it to nil. So it should be safe to call.
PS: Is there some way to look at the source code of FliteController.m? I just want to look at the implementation to find out what the methods in the header file do. I don’t want to modify anything. For e.g. I want to find out how AVAudioPlayerDelegate is implemented etc.