Two mass graves containing the ashes of at least 8,000 Polish people murdered by the Nazis during World War II have been discovered in a forest north of Warsaw.
Special investigators in Poland said at least 17 tonnes of human ashes were found.
The victims were mostly inmates of the German-run Soldau concentration camp, in the Polish town of Dzialdowo, who were executed in the forest between 1940-44, the experts said.
In March 1944 the bodies were dug up, burned and trees were planted over the burial pits in an attempt to hide the atrocity.
Investigators from the Institute of National Remembrance marked the finding this week with speeches and wreath-laying at the site in the Bialuty Forest, 160 kilometres north of the Polish capital.
The institute's Karol Nawrocki said the bodies had been "brought out, burned and pulverised in order to prevent this crime from ever being known, in order to prevent anyone taking responsibility for it".
"These efforts were not successful," he said.
The Nazis used other inmates, mainly Jewish, to do the cover-up job. Those inmates were also killed.
Institute experts said the ashes were found in two pits each 3 metres deep.
An estimated 30,000 people, mostly Polish political prisoners, soldiers, resistance fighters and Jews were inmates at the camp and many of them were killed or died in the Nazis' plan of extermination.
The forest was already known to be the site of burials, but the exact location of the mass graves and the number of the victims were not known until now.
Archaeologists and anthropologists located the two mass graves this month.
The institute investigates Nazi crimes and also communist crimes against Poles and has the power to bring charges against the suspects if they are still alive.
ABC/AP