Translate the following English sentence to French:
"I became convinced of this in Sarajevo when I had to negotiate the periodic exchanges of prisoners which accompanied each successive ceasefire agreement, none of which unfortunately lasted, between the parties to the conflict."
De cela je me suis convaincu à Sarajevo quand j' avais à agir pour négocier, entre les parties au conflit, les échanges périodiques de prisonniers, qui accompagnaient chaque accord successif de cessez-le-feu, malheureusement jamais durable.