 Complete the following phrase:  There is strong evidence that the central Soviet authorities deliberately refrained from a larger accumulation of partisan forces in western Belarus and let Polish underground military structures grow in these lands during 194142 in order to strengthen Moscows relations with the Polish government-in-exile of Władysław Sikorski. A certain level of military cooperation, imposed by the command headquarters, was noted between Soviet partisans and the Polish Home Army, Armia Krajowa AK. Soviet partisans avoided to some extent attacking people of Polish nationality during the terror campaigns in 1942. After the breakdown of diplomatic relations between the USSR and the Polish government-in-exile in April 1943 resulting from the discovery of the Katyn massacre which the 