BERLIN (Reuters) - Previously unknown paintings by Marc Chagall and Otto Dix are among a vast trove of Nazi-looted art found in a Munich apartment that includes works by some the 20th century's most celebrated artists, German experts said on Tuesday.
Customs investigators seized the 1,400 artworks, dating from the 16th century to the modern period and by artists such as Canaletto, Courbet, Picasso and Toulouse-Lautrec, last year, an official said.
While experts consider the works to be of huge artistic value, the task of returning them to their rightful owners could take many years and poses a huge legal and moral problem for the German authorities.
The haul, found in the flat of Mr Cornelius Gurlitt, the reclusive son of a wartime art dealer, is one of the most significant discoveries of works looted by the Nazi regime and could be worth more than US$1 billion (S$1.24 billion), according to a German magazine.
Mr Gurlitt has since vanished and the authorities have not explained why it has taken them about a year to announce the massive find. The paintings, which were found in generally good condition, are being stored in an undisclosed location and they will not be published online.
"When you stand in front of works that were long considered lost, missing or destroyed, and you see them again, in a relatively good condition - a little bit dirty but not damaged - it's an incredible feeling of happiness," said Mr Meike Hoffmann, an art expert from Berlin's Free University who has been assessing the find.
The Nazis systematically plundered hundreds of thousands of art works from museums and individuals across Europe. Thousands of works are still missing.
Investigators chanced upon the art after Mr Gurlitt, believed to be in his seventies, aroused their suspicions as he travelled by train between Zurich and Munich, carrying thousands of euros in cash, according to German media. He has since disappeared.
"We cannot say where the accused is, we do not know ourselves," said Mr Reinhard Nemetz of the public prosecutor's office in Augsburg.
Jewish groups have urged that the origins of the art works be researched as quickly as possible, so that, if looted or extorted, they can be returned to their original owners.
For some families missing art constitutes the last personal effects of relatives murdered during the Holocaust.
Officials declined to comment on the value of the art.
Germany's Focus magazine, which revealed the find and prompted the authorities to go into the open, said it could be worth over 1 billion euros (S$1.68 billion).
"We were able to confiscate 121 framed artworks and 1285 non-framed works, including some famous masterpieces," Mr Nemetz said. "We had concrete clues that we were dealing with so-called 'degenerate art', or so-called looted art."
Mr Gurlitt's father Hildebrand Gurlitt was, from 1920, a specialist collector of the modern art of the early 20th century that the Nazis branded as un-German or "degenerate" and removed from show in state museums, or displayed simply to be mocked.
Nazi propaganda minister Joseph Goebbels recruited Gurlitt to sell the "degenerate art" abroad to try to earn cash for the state. Gurlitt bought some for himself and also independently bought art from desperate Jewish dealers forced to sell.
Investigators said the collection comprises works which are clearly from the Nazi regime's state-owned collection of"degenerate art". Others, which may have had several owners or may have been extorted from owners fearing Nazi persecution, will need extensive research.
Mr Siegfried Kloeble, from Munich's customs investigation office, said media reports that authorities had failed to disclose the find for two years were wide of the mark. The search took place in 2012, and not, as reported, in 2011.
Mr Hoffmann said that among the previously unknown paintings was a self-portrait by Dix, in impeccable condition, and probably painted around 1919.
A similarly unknown Matisse painting, of a seated female figure that he painted several times, probably dated from the mid 1920s and was confiscated in 1942.
Germany has faced criticism that the restitution process is too complicated and lacks sufficient funding. Mr Nemetz said there were no plans to publish a list of the works online and people should come forward with inquiries.
Jewish restitution groups have often criticised state and museum authorities for not doing enough to research works'origins themselves and instead leaving the onus on relatives.