Relatives of Raoul Wallenberg have filed a lawsuit against Russia's Federal Security Service (FSB) to provide uncensored documentation that could help determine the fate of the former Swedish diplomat and war hero.

Wallenberg, who saved thousands of Hungarian Jews from slaughter during World War II, was captured by Soviet forces in 1945 and died two years later in prison.

Russia has only said that Wallenberg died in 1947 in Moscow's notorious Lubyanka prison, which was run by the KGB security service, although details of the death remain unclear. The FSB is the successor agency of the KGB.

Wallenberg's niece, Marie Dupuy, said on July 26 that she had asked the Russian legal association Team 29 to file suit in a Moscow court because "numerous requests to Russian authorities over many years, publicly and privately, by myself, by expert historians, and Swedish officials, have failed to yield any results."

Dupuy claimed Russian archives contained documents with direct relevance related to Wallenberg's fate but said his family and independent experts have not been allowed to examine the documents.

"Our search for answers will continue until we know what happened to Raoul Wallenberg, and why," Dupuy said.

The FSB did not immediately respond to requests for comment.

Based on reporting by AP and Reuters

