MOSCOW, October 27 (RIA Novosti) - The top Polish representative on a bilateral commission on Russia and Poland's joint history urged Moscow on Monday to open up archives on the World War II Katyn massacre.

More than 20,000 Polish military officers, police and civilians taken prisoner during the 1939 partitioning of Poland by the Soviet Union and Nazi Germany were massacred by the NKVD, the forerunner of the KGB, in the Katyn forest and at other locations.

Former foreign minister Adam Rotfeld said the Katyn issue was "poisoning relations" between the two countries, and that without openness on the subject, the commission "would not be able to move further."

"Historians have done a lot, many books have been written, but there are issues that demand the disclosure of the archives, and a political-level decision is necessary here," he said.

He also said the commission, which is a bilateral group that discusses the complex questions of history between the two countries, would do its best to have the archives opened.

On Friday, a Moscow court refused to exonerate the Katyn victims.

In 2005, the Chief Military Prosecutor's Office closed the "Katyn Case," saying those involved in the executions had since died. However, the relatives of the executed officers appealed the decision to close the case.

The Soviet Union initially accused Germany of executing the Polish prisoners. However, in 1990 Mikhail Gorbachev officially admitted that Soviet secret police were responsible for the massacre.