The Shelling of Mainila (, ), or the Mainila incident (), was a military incident on 26 November 1939 in which the Soviet Union's Red Army shelled the Soviet village of Mainila () near Beloostrov. The Soviet Union declared that the fire originated from Finland across the nearby border and claimed to have had losses in personnel. Through that false flag operation, the Soviet Union gained a great propaganda boost and a casus belli for launching the Winter War four days later. Historians have now concluded that the shelling of Mainila was a fabrication carried out by the Soviet NKVD state security agency. Background The Soviet Union had signed international and mutual nonaggression treaties with Finland: the Treaty of Tartu of 1920, the Non-aggression Pact between Finland and the Soviet Union signed in 1932 and again in 1934, and further the Charter of the League of Nations. The Soviet government attempted to adhere to a tradition of legalism, and a casus belli was required for war. Earlier in the same year, Nazi Germany had staged the similar Gleiwitz incident to generate an excuse to withdraw from its nonaggression pact with Poland. Also the Soviet war games held in March 1938 and 1939 had been based on a scenario where border incidents taking place at the village of Mainila would have sparked the war. The incident Seven shots were fired, and three Finnish observation posts detected their fall. These witnesses estimated that the shells detonated approximately inside Soviet territory. Finland proposed a neutral investigation of the incident, but the Soviet Union refused and broke diplomatic relations with Finland on November 29. Materials in the private archives of Soviet party leader Andrei Zhdanov show that the incident was orchestrated to paint Finland as an aggressor and launch an offensive. The Finnish side denied responsibility for the attacks and identified Soviet artillery as their source—indeed, the war diaries of nearby Finnish artillery batteries show that Mainila was out of range of all of them, as they had been withdrawn to prevent such incidents. The Soviet Union then renounced the non-aggression pact with Finland and on 30 November 1939 launched the first offensives of the Winter War. Aftermath John Gunther, an American journalist and author wrote in December 1939 that the incident "was as clumsy and obviously fabricated as all such 'incidents' have been since Mukden in 1931". The Finns conducted an immediate investigation,