 In April 1938 , an NKVD agent , Boris Yartsev contacted the Finnish foreign minister Rudolf Holsti and Prime Minister Aimo Cajander , stating that the Soviet Union did not trust Germany and that war was considered possible between the two countries . The Red Army would not wait passively behind the border but would rather " advance to meet the enemy " . Finnish representatives assured Yartsev that Finland was committed to a policy of neutrality and that the country would resist any armed incursion . Yartsev suggested that Finland cede or lease some islands in the Gulf of Finland along the seaward approaches to Leningrad ; Finland refused . 
