I boken "Die Sowjetunion und das Dritte Reich: Eine dokumentierte Geschichte der deutsch-sowjetischen Beziehungen von 1933 bis 1941" nämns
The Russians consider that the Americans, once they have completed their armament, will possess a force that will be able to inflict decisive blows on the Japanese. For the time being they are treating the Germans and Japanese with cautious restraint. At the moment when the Americans have driven the Japanese into a corner in a serious way and the British have done the same to the Germans, the Russians will also start to strike out against both the Germans and the Japanese. The Russians are immersed in strong military preparations in order to defend themselves against a combined strike by the Germans and Japanese in the Spring [of 1941]...........As soon as the British become stronger in the areas of Turkey, Iran, Afghanistan and Irak, or to express it better, as soon as they have strengthened their military force in the Near East in combination with those states, they will provide a breathing space for the Soviets to a large degree.......As I have indicated above, the Soviets will wait for Britain and America to complete their preparations. Then they will probably go over to active operations together with them.