The Federal Archive Agency posted documents Wednesday for the first time on the Internet about the Soviet Union’s World War II massacre of more than 20,000 Polish officers and other prominent citizens.

President Dmitry Medvedev ordered the documents posted on the archives’ Russian-language web site, reflecting a new willingness in Russia to accept responsibility for the killings at Katyn and elsewhere in 1940.

Relations between Russia and Poland have warmed following the tragic April 10 plane crash that killed Polish President Lech Kaczynski, his wife and 94 others on a flight to visit the Katyn forest near Smolensk for a memorial ceremony on the 70th anniversary of the massacre.

But while Medvedev’s order was clearly intended as a positive gesture, the documents posted Wednesday were made public long ago and already have been published in Poland and Russia. Many more documents remain classified, despite dogged Polish appeals for the archives to be opened.

Medvedev later promised that more documents would be released.

“There is some material that has not yet been handed over to our Polish partners. I have given the order to make that happen,” he told journalists in Copenhagen.

The Katyn documents would help people learn from history, he said.

“Let everyone know what was done, who made the decisions, who ordered the elimination of the Polish officers,” he said. “Everything is written there. With all the signatures.”

The documents now on the Internet were made public in 1992 by former President Boris Yeltsin and include a March 1940 letter by Lavrenty Beria, head of the secret police, recommending the execution of the Polish prisoners of war. The letter bears the signatures of Soviet dictator Josef Stalin and three other members of the Politburo.

The documents also include the minutes of a Politburo meeting on March 5, 1940, and a note from the head of the Soviet secret police in 1959 informing Soviet leader Nikita Khrushchev that the Katyn files had been destroyed.

For 50 years, the Soviet Union blamed the massacres on the Nazi German forces who invaded in 1941. This remained the official line until Soviet leader Mikhail Gorbachev acknowledged Soviet responsibility in 1990, but Poles had always known the truth and the cover-up fed animosity toward Russia.

Documents that remain classified include materials from an investigation in the 1990s that are believed to include the names of those who carried out the executions.

Russia also has refused Polish requests to recognize the executed Poles as victims of political repression.

Polish historian Andrzej Kunert said that although the documents posted Wednesday were known to historians, the decision to post them on the Internet was significant. “We can surely call the decision a breakthrough because it seems that for the first time a web site that is generally accessible to everyone in the Russian Federation publishes three very important documents concerning the Katyn massacre,” Kunert said on Polish TVN24. “It is certainly a very important step forward.”

The Memorial rights organization, which brought the appeal, welcomed Wednesday’s posting of the documents but said it was only a small step. “The files of this criminal case must be disclosed and procedures observed, giving the Polish POWs executed in Katyn the status of victims of political repression,” said Alexander Guryanov of Memorial, Interfax reported.