Russia and Poland continue cautious rapprochement

Mr Medvedev had earlier in the day told the press while on a visit to Denmark: "There is a series of materials, which we have not yet given [to Poland]."

Josef Stalin's secret police, the NKVD, in 1940 executed 22,000 Polish officers and intellectuals in the forests close to the town of Katyn in western Russia.

Russia in the 1990s first admitted responsibility for the massacre and declassified some documents, such as Stalin's signature on a letter recommending the killings by NKVD chief Lavrentiy Beria. But it has kept secret other papers, such as a list of the identities of thousands of Poles murdered by the NKVD in Belarus, feeding mistrust. The Soviet slayings are seen on a par with Nazi crimes by many in Poland.

Polish angst over Katyn was stirred deeply earlier this month when a plane crash killed Polish president Lech Kaczynksi and 95 members of his delegation en route to a Katyn commemoration in Russia.

Mr Medvedev on Wednesday ordered the already-disclosed Katyn files to be published on the internet, with over 2 million people quickly flocking to the website.

The internet publication was widely-covered by Russian media and will help to undermine Katyn-massacre-deniers in Russia.

"It's another important step. I doubt that the Communists will stop saying what they are saying, but their credibility will now be much smaller," Andrei Artizov, the head of the Russian archives depository, said, Poland's Gazeta Wyborcza reports.

Poland's testy relationship with Russia has in recent years seen Warsaw veto an EU-Russia political pact and try to scupper plans for a new Russia-Germany gas pipeline, with the late Lech Kaczynski and his twin brother, Jaroslaw, chief in the Russia-hostile class in the Polish establishment.

The Tusk government has over the past two years tried to normalise relations with Moscow and to come in out of the cold in terms of the EU's collective approach to its giant neighbour.

Russia's sensitive handling of the Smolensk plane tragedy has helped the cautious rapprochement between the two states to make further progress in recent weeks, with Mr Tusk on Wednesday also thanking Russia for its openness in the air crash probe.

"We have no reasons to say that on the Russian side there were attempts to obfuscate the investigation," he said.

Poland is to hold snap presidential elections on 20 June, with Bornislaw Komorowski, from Mr Tusk's ruling centre-right Civic Platform party, expected to trounce his main contender, Jaroslaw Kaczynski, by 60 percent to 34 percent, according to pollsters.