The bombing of Kassa took place on 26 June 1941, when still unidentified aircraft conducted an airstrike on the city of Kassa, then a part of Hungary, today Košice in Slovakia. This attack became the pretext for the government of Hungary to declare war on the Soviet Union the next day, 27 June. On 26 June 1941, four days after Germany attacked the Soviet Union in violation of the Molotov-Ribbentrop non-aggression treaty, three unidentified planes of apparently Soviet origin bombed the city, killing and wounding over a dozen people and causing minor material damage.