COPENHAGEN (AFP) - Russian President Dmitry Medvedev said Wednesday he had ordered the publication of files on a 1940 massacre of Polish officers by Soviet secret police because "we owe it to the world."

• First Russian state visit to Denmark in 45 years

"We must learn the lesson of history," Medvedev told reporters during a state visit to Denmark.

Earlier Wednesday, files on the massacre at Katyn were on Medvedev's orders published on the Internet, in an unprecedented move aimed at improving relations with Poland.

"Showing these archives (today) does not mean that they were hidden" previously," the Russian president told a joint press conference with Danish Prime Minister Lars Loekke Rasmussen.

"This simply means that this material ... has been put up on our archive website to allow everyone the possibility to see who gave the orders to kill the Polish officers," he said.

"Everything is in the documents. All the signatures are there. All the people are known," he added.

The documents in question had been declassified in September 1992 on the orders of then-president Boris Yeltsin and shared with Poland, the statement said.

But until now the originals had only been available to researchers visiting the archives and had never before been shared online, a spokeswoman for the Russian state archives told AFP.

Some 22,000 Polish officers were executed by Stalin's secret police at Katyn, in western Russia, and a number of other sites in present-day Russia, Ukraine and Belarus in April-May 1940.

The officers had been taken prisoner after the Soviets invaded and occupied eastern Poland in September 1939, dividing up the country under the terms of a secret pact with Nazi Germany, which seized the rest of Poland.