The Soviet government immediately denied the German charges. They claimed the Polish prisoners of war had been engaged in construction work west of Smolensk, and consequently were captured and executed by invading German units in August 1941. The Soviet response on 15 April to the initial German broadcast of 13 April, prepared by the Soviet Information Bureau, stated "Polish prisoners-of-war who in 1941 were engaged in construction work west of Smolensk and who...fell into the hands of the German-Fascist hangmen". In April 1943, the Polish government-in-exile led by Sikorski insisted on bringing the matter to the negotiation table with the Soviets and on opening an investigation by the International Red Cross. Stalin, in response, accused the Polish government of collaborating with Nazi Germany and broke off diplomatic relations with it. The Soviet Union also started a campaign to get the Western Allies to recognize the pro-Soviet government-in-exile of the Union of Polish Patriots led by Wanda Wasilewska. Sikorski died in the 1943 Gibraltar B-24 crash —an event convenient for the Allied leaders.