The European Court of Human Rights said Monday it cannot rule on whether or not Russia properly investigated a World War II massacre of thousands of Polish officers because it has not received vital documents from Moscow to properly judge the case.

The court also said it considers the massacre in the Katyn forest a "war crime," but that it cannot force Russia to further investigate. Poland considers it a war crime, but Moscow has refused to apply the term.

The court found Russia in violation of the European Convention for Human Rights for refusing to share investigation documents, and said that Russia's response to most attempts by victims' relatives to find out the truth about what happened had amounted to "inhuman treatment."

Fifteen Poles have complained that Russia failed to hold a proper investigation or to find those responsible for the 1940 killing by the Soviet secret police of some 22,000 Polish officers and intellectuals in the Katyn forest and other places.

The Katyn massacre has been a sore point in Russia-Poland relations for decades since 1943, when the Soviet Union blamed the killings on the Nazis. It was in 2010 that Russia formally took the blame when the lower chamber of Russia's parliament admitted the executions were ordered by Soviet leader Josef Stalin.

In the 1990s, Russia launched an investigation into the killings, but discontinued it in 2004. It refused to make its reasoning available to the relatives or to the European court.

In Moscow, Russia's Justice Ministry reported Monday's ruling without comment.

But Poland's government said the case shows Russia's disregard for international law.

"It is not for the first time that Russia has a problem with following the standards of a European state of law," said Justice Minister Jaroslaw Gowin said on Polish TVN24.

One of the 15 Polish relatives, Ryszard Adamczyk, said that officials in Russia have "their own laws, they disregard international laws."

In Moscow, Leonid Slutsky, the chairman of the committee in charge of relations with the former Soviet nations in the lower house of parliament, said the European Court of Human Rights had tried to walk a middle line in its ruling.

"The judges apparently sought to partly satisfy the Polish party without hurting Russia too much," Slutsky said, according to the RIA Novosti news agency. He said the issue requires deeper consideration, adding that he wasn't sure that the judges had studied all materials available.

Slutsky said the court ruling is unlikely to have any impact on Russian-Polish ties, saying that while the issue remains an irritant, relations between Moscow and Warsaw are gradually becoming more constructive thanks to economic cooperation.

___

AP writers Monika Scislowska in Warsaw and Vladimir Isachenkov in Moscow contributed to this report.