THE HAGUE (AFP).- Two researchers in the Netherlands have raised doubts about a rare watercolour painting signed by Adolf Hitler, saying it appears more likely to be the work of a forger, a Dutch newspaper reported Wednesday.
"It is very probably a fake Hitler" painting, Bart Droog and Jaap van den Born, both specialists in tracking imitations of Hitler's artwork, told the daily De Volkskrant.
The aquarelle -- a technique of painting with thin transparent watercolours -- depicting a tower in Vienna had been donated this year to the Amsterdam-based NIOD wartime institute by a woman whose identity was not revealed.
The woman's father originally bought the painting at a stamp and coin market for 75 cents and only realised when he got home that it was signed by "A. Hitler", media reported in November when news of the donation became known.
"After months of following an authentication process the... conclusion is: it's an original from the hand of Adolf Hitler," the NIOD said in a statement at the time, putting the work by a young Hitler between 1909 and 1913.
In response to the latest questions about its authenticity, the institute issued a statement saying it "takes these comments seriously and is open to critical reactions to our research".
It added that the institute's conclusions that the painting appeared authentic were only "provisional".
"We are going to continue the research," said the NIOD institute's director Frank van Vree, adding that he wasn't sure "to be able one day to find definitive proof".
According to Droog and Van den Born, the watercolour could have been done by Reinhold Hanisch, a well known forger of the Nazi dictator's artwork.
The painting, which art critics have described as "mediocre", even "ugly", was given to the NIOD, originally set up just after World War II to create a national archive of documents relating to the 1940-45 Nazi occupation of The Netherlands, after two Dutch auction houses refused to put it up for sale.
The Netherlands was occupied for around five years by the Nazis, who carried out a reign of terror, including deporting more than 100,000 Jews to death camps such as Auschwitz and Sobibor where they were murdered.
The victims included world-famous Dutch teenaged diarist Anne Frank and most of her family.
Most of Hitler's artworks are now in private collections in Austria, Britain, Germany and the United States, and the US Army still has four works which it confiscated during the war.
© Agence France-Presse