A Strange Duel(1971)

Original title: Странен двубой

In a bustling European city, Bulgarian agent Pavlov, under suspicion of double-dealing in a Western spy center, is exonerated and assigned to lead a covert operation alongside colleague Robert Houston. Tasked with recruiting a Bulgarian contact as part of a larger plan to neutralize missile sites at home, Pavlov and Houston are sent to Bulgaria, where their mutual distrust fuels a dangerous game.