A court in Moscow has turned down a lawsuit by the relatives of Raoul Wallenberg, the Swedish diplomat who disappeared after helping at least 20,000 Hungarian Jews escape the Holocaust.

The lawsuit demanded that the KGB's main successor agency provide full and uncensored documentation about his case.

The Swedish diplomat is believed to have died in Soviet captivity, but the time and circumstances of his death have remained unclear.

Wallenberg's niece, Marie Dupuy, had asked a Russian legal association to file the lawsuit, arguing that numerous requests to Russian authorities for information have been fruitless. Moscow's Meshchansky Court rejected the lawsuit Monday.

Wallenberg vanished after being arrested by the Red Army in 1945. The Soviets initially denied he was in their custody, but later said he died in prison in 1947.