Very obvious that several people making strong and assertive statements in this thread are not and never have been commercial pilots, a few more know little or nothing about explosives and how to detonate them.
There are and have been for a very long time a clear set of rules for an intercept, not going into details here but commercial pilots all know what to expect and then what to do if they discover they have a fighter aircraft formating on their left hand side and endeavoring to communicate with them. There are certain visual signals and maneuvers that will leave the civilian aircraft in no doubt as to what is to happen next, these are all internationally agreed and (should) be well known to all commercial pilots regardless of their nationality. There are major and obvious differences between an aircraft following it's flight plan but has simply lost comms. and one that has deviated without clearance and is maneuvering in an unusual or suspicious way.
It is only after all recognised attempts to communicate have failed and the aircrafts intentions remain threatening that any action would be taken. As I thought I made clear at the beginning, these rules have all been revisited since September 2001.