Situated on the premises of a defunct customs warehouse and a former army barracks, Stalag XVIII D was set up right after the capitulation of the royal Yugoslav army and the German occupation of Slovenia's second city.

The first mention of the facility in German documents dates back to 1 June 1941, when the camp housed 3,838 Yugoslav and 208 British POWs. The last written mention of 1 October 1942, lists 6,180 French, 2,812 Brits, two Yugoslavs and 2,450 Soviet POws.

Soviet POWs, who numbered more than 5,000 at one time, were treated with special cruelty and most of them died in the camp. They were detained separately in the defunct customs warehouse ravaged by typhus.

"The conditions in which the Soviet POWs lived were no less horrendous than those in the worst Nazi concentration camps such as Dachau, Auschwitz and Mauthausen," a Slovenian historian has told the STA.

"The prisoners were starved. More than 5,000 men didn't have their own kitchen, latrines and they slept on the floor. Most of the guards beat them sadistically," National Liberation Museum Maribor director Aleksandra Berberih Slana said.

The locals tried to help the prisoners and possibly loves of bread handed to them in secret by a shop owner might have saved some of them, but this was just a drop in the ocean with Berberih Slana estimating that several thousand perished there.

The museum she heads and the Maribor city authorities has been working with the Russian Embassy in Ljubljana to revive the memory of the camp and its inmates ahead of the 70th anniversary of the end of WWII in 2015.

The only reminder of the history of the empty customs warehouse is a memorial plaque unveiled there in September 2011 and which last year saw a visit by a Russian delegation.

A virtual presentation of a museum that is to be put up there will be held on 8 July along with a small exhibition. The Russian delegation to the event is expected to include Foreign Minister Sergey Lavrov.