The remains of more than 20 suspected victims of Joseph Stalin's secret police have been found in the basement of a church in northern Belarus.
Soviet bullets were found with the remains at Glubokoye, a village which had been in Poland but fell into Soviet hands in 1939.
A youth group discovered the remains earlier this week, reports say.
Local historians said the victims had most probably been shot by the NKVD secret police between 1939 and 1941.
"I think we can all but rule out any suggestion that these people were shot by the Germans during the occupation," historian Igor Kuznetsov told Reuters.
"First, there are the cartridge cases from Soviet weapons. Second, the Germans carried out public executions and these people were killed in secret, in a manner typical of the NKVD."
Soviet forces occupied eastern Poland in 1939 after the signing of the Nazi-Soviet Non-Aggression Pact. Nazi Germany invaded the Soviet Union in June 1941.
In 1940, more than 21,000 Polish army officers and intellectuals were executed on Stalin's direct orders in the Katyn Forest near the city of Smolensk, in western Russia.
For decades, the Soviet authorities blamed Nazi Germany for the Katyn massacre.