The Soviet Union had been discontented with the Baltic states leaning toward Britain and France , the so-called Baltic Entente dating back to 1934 , which could potentially be reoriented toward Germany , and considered it a violation of the mutual-assistance treaties of the autumn of 1939 . On May 25 , 1940 , after several Soviet soldiers had disappeared from Soviet garrisons in Lithuania , Molotov accused the city of Kaunas of provocations . On June 14 , People 's Commissar of Defence Timoshenko ordered a complete blockade of Estonia , Latvia , and Lithuania . The Soviet air force shot down a Finnish passenger plane Kaleva heading from Tallinn towards Helsinki . Shortly before midnight , Molotov presented Lithuania with a ten-hour ultimatum , demanding the replacement of the Lithuanian government with a pro-Soviet one and free access for additional Soviet troops , threatening the country with immediate occupation otherwise
Kaleva
Kaleva (airplane)
Germany–Soviet Union relations, 1918–1941