 On 5 October 1939 , the Soviet Union invited a Finnish delegation to Moscow for negotiations . J.K. Paasikivi , the Finnish ambassador to Sweden , was sent to Moscow to represent the Finnish government . The Soviets demanded that the border between the USSR and Finland on the Karelian Isthmus be moved westward to a point only 30 km ( 19 mi ) east of Viipuri and that the Finns destroy all existing fortifications on the Karelian Isthmus . They also demanded the cession of islands in the Gulf of Finland as well as the Kalastajansaarento peninsula . Furthermore , the Finns would have to lease the Hanko Peninsula for thirty years and permit the Soviets to establish a military base there . In exchange , the Soviet Union would cede two municipalities with twice the territory demanded from Finland . Accepting Soviet demands would have forced the Finns to dismantle their defences in Finnish Karelia . 
