The Mossad conducted operations that were definitely not considered legal by the majority of countries. However, the only operation I can think of which involved an actual assassination was the assassination of Herbert Cukurs in Uruguay.

Perhaps not entirely what you're asking for, but in Denmark, a country which had been occupied by the Germans for most of the war, people sought out girls who had fallen in love with German soldiers. They would then publically shame them, cut off their hair, call them "field matresses" and a number of other not so nice things.

AFAIK no girls were actually killed though.