A group representing Jews caught up in the Holocaust and their descendants has called for the publication of a list of the works found at the Austrian home of the son of a Nazi-approved art dealer.
Dozens of works emerged at the home of Cornelius Gurlitt near Salzburg on Tuesday.
The Jewish Claims Conference said that a list must be published to find the rightful owners or their heirs.
Mr Gurlitt is the son of the Nazi-approved art dealer Hildebrand Gurlitt and his collection is suspected to include works stolen or extorted from Jewish owners.
A spokesman for Mr Gurlitt, 81, said on Tuesday that experts were examining the 60 works to see if they were stolen during the Nazi era.
"The prerequisite for any restitution is the publication. Otherwise, survivors and their families cannot register claims," the Claims Conference said.
But Mr Gurlitt's spokesman Stephan Holzinger is reported to have turned down the request swiftly, claiming that an initial analysis appeared to suggest that none of the works was stolen or extorted by the Nazis.
"It's a private collection," Mr Holzinger told the AFP news agency. "If one were to follow that logic, all the collections in Germany would have to be published."
When asked how much the recently discovered objects were worth, Mr Holzinger said the objects are largely oil paintings "on average of greater value than those discovered in Munich".
The Claims Conference's representative in Germany, Ruediger Mahlo, said in a statement that as Mr Gurlitt is the son of "one of the four art dealers commissioned by Hitler to handle stolen art... therefore the origins of his inheritance should be checked.
More than 1,400 long-lost or unknown art works, estimated to be worth $1.35bn (£846m) were discovered in Mr Gurlitt's apartment in Munich in March 2012.
They included pieces by Marc Chagall, Pablo Picasso, Henri Matisse, Otto Dix and Max Liebermann.
But details of the find only came to light last year, sparking criticism of the German authorities for not publicising the discovery sooner.