Russia has provided Poland with 11 volumes of declassified documents on the 1940 massacre of more than 20,000 Polish officers and others by the Soviet secret police.
Today's handover at Russia's Prosecutor-General's Office brings the total number of declassified volumes given to Poland to 148.
A statement on the prosecutor's website says the 11 volumes refer to the criminal records and place of burial of the victims.
Russia's long-delayed cooperation on the wartime killings has helped mend ties between Moscow and Warsaw.
The Soviets falsely blamed the Katyn massacre on the Nazis for years, before Mikhail Gorbachev acknowledged the Soviet role in 1990.
compiled from agency reports