They can monitor the bit in between, but there are laws about using tracking devices which monitor other countries air traffic, also some are that powerful that they can pick up mobile phones broadcasting on the same frequency.
As when i was in the Army in Afghanistan, we had a runway at Camp Bastion for troop flights and UAV (unmanned) and because the Britiish Army is skint the Americans lent us one of thier RADAR devices, however it ended up that we had a visit from the Japanese Embassy in Kabul (Afghan Capital) because it was monitoring thier Military Air Traffic.
I only know about this as the Army is massive on "passing the buck" and as RMP (Military Police) we get given any crap task when no-one else knows what to do, so me and two collegues had to meet with the Japanese Ambassador to Afghanistan, whilst we waited for the British Embassy guys to turn up, luckily they spoke a bit of english.
In the end we had to get a tacky German one, and there were no flights for 3 days, as it had to be turned off.
True Story.
