Amsterdam - Police in the Netherlands were on Monday investigating the cause of a fire that destroyed the barracks that housed Anne Frank in the former concentration camp of Westerbork during the Holocaust.

The current owner of the barracks, Jan Egges, told journalists that he suspects arson as "there was nothing in the shed that could have caused the fire" that started Sunday. Officials from the fire brigade said the barracks had housed only agricultural machinery.

Anne Bitterberg of the Westerbork memorial museum told the German Press Agency dpa that the barracks had been due to be moved from the farm in Veendam where it was being stored to the former camp site in a month's time.

"All building permits had been arranged and the contractor was hired as well," she said. "This is dramatic."

Attempts to return the structure to Westerbork had been under way for almost 20 years.

The daily Volkskrant, meanwhile, on Monday reported that shortly after plans for the barracks' return to its original site was announced, anonymous messages were published on a local website threatening to burn it down.

"This was important heritage from World War II," said museum director Dirk Mulder.

"Westerbork has no more barracks today. We had the opportunity to return one in its original form. This is a major loss."

According to historic documents discovered recently, Frank and her sister Margot had performed slave labour in one of the barracks at Westerbork in 1944.

The camp was built in the 1930s to house German Jewish refugees. During WWII, it became a Nazi concentration camp for Dutch Jews, from which 104,000 Jews were deported to camps in Germany and Poland, where more than 80 per cent were murdered.

After WWII, the camp served as prison for Dutch Nazi collaborators and later asylum seekers.

Between the 1950s and 1971, when the camp became a memorial museum, all barracks were sold. The Anne Frank barracks that burnt down on Sunday had been to a farmer in 1957.

Born in Frankfurt in 1929, Annelies Marie Frank fled with her family to the Netherlands after the Nazis' rise to power in 1933.

In 1942, the Frank family went into hiding with four other Jews in the annex of a house on Prinsengracht 263 where the teenager Anne kept a diary.

In early August 1944, she and all others were betrayed and deported to Westerbork and several weeks later, to Auschwitz. Frank died in Bergen-Belsen in 1945.

Only her father Otto Frank survived. In 1947, he published his daughter's diary, which had been saved by members of the resistance. The book became an instant publishing success. (dpa)