A government newspaper published a secret document Thursday indicating the Soviets were responsible for the massacre of thousands of Polish officers in the Katyn woods during World War II.

The Soviets blamed the Germans for the execution-style killings on Soviet territory, but the report said documents found on the bodies indicated the officers were killed between the end of March and the beginning of May 1940. The Soviet Union was attacked by the Nazis in June 1941.The government newspaper Odrodzenie said the secret document prepared by the Polish Red Cross in 1943 recently was found by a Polish historian in the British archives.

The Nazis unearthed the mass graves containing the officers' remains in 1943 and invited international experts, including the Polish Red Cross based in London, to make an on-site inspection.

According to the Red Cross document, the remains of 4,243 Polish officers were found in the mass grave of Katyn near Smolensk following the exhumation in 1943.

"The documents found with the bodies indicate that the murder took place between the end of March and the beginning of May 1940," Odrodzenie said.

Thousands of Polish officers were evacuated deep into Soviet territory following the Soviet attack on Poland in 1939.

The Katyn crime has been avoided in the Polish news media for more than four decades until the emergence of Soviet leader Mikhail Gorbachev's policy of glasnost, or openess.

Poland and the Soviet Union formed a joint commission of historians two years ago to explain the crime, but progress has been slow with the Soviets complaining they did not have enough evidence to back up an admission of guilt.