MOSCOW (AP) — Russia's state archives posted documents on the Internet for the first time Wednesday about the Soviet Union's World War II massacre of more than 20,000 Polish officers and other prominent citizens.

The step was a gesture to Poland in a case that looms large in Polish history and has soured relations between the two countries for decades.

President Dmitry Medvedev ordered the documents posted on the archives' Russian-language website, 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 in western Russia 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."

In Warsaw, Poland Prime Minister Donald Tusk was cautiously optimistic, saying he welcomed the sentiment but would await Russia's next step.

Kaczynski's death could be a catalyst for renewed co-operation between Warsaw and Moscow, and Tusk urged Russia not to let the opportunity slip.

"I am curious to see if Russia will use the chance that this tragedy has given," Tusk told a news conference. "Let's wait for facts."

The documents now on the Internet were made public in 1992 by Boris Yeltsin, Russia's first post-Soviet leader. They 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 the Politburo meeting on March 5, 1940, at which Beria's proposal was approved, and a note from the head of the Soviet secret police in 1959 to Soviet leader Nikita Khrushchev advising that the Katyn files be 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. It was not clear whether Medvedev planned to release these materials.

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

Polish historian Andrzej Kunert said 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 website 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."

Many Russians still do not know the truth about Katyn, and the release of the documents may play a positive role in helping Russians come to terms with their own painful history under Stalin.

Within hours of the posting of the documents, nearly 700,000 Internet users tried to access the website, the ITAR-Tass news agency reported, citing a spokesman for the state archives. The website responded slowly throughout the day due to the continued heavy traffic.

Kunert stressed that Poles were still waiting to see the results of the investigation by Russian prosecutors, and especially the classified reasons behind the discontinuation of the investigation in 2004.

Russia's Supreme Court took a small step in that direction last week by ordering the Moscow City Court to consider an appeal calling for the prosecutor's decision to drop the investigation to be declassified.

The Memorial rights organization, which brought the appeal, welcomed the posting of the documents on the government website, 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," Alexander Guryanov of Memorial said, according to the Interfax news agency.

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On the Net: http://rusarchives.ru/publication/katyn/spisok.shtml

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Associated Press writers Monika Scislowska in Warsaw, Poland, and Jan M. Olsen in Copenhagen contributed to this report.