Allied troops seized more than 100 art works in 1945 from the German dealer and collector whose trove came to light this week, then gave them back about four years later, a US researcher said on Wednesday.

Marc Masurovsky, who is part of a group that works to return Nazi-looted art to its owners, said documents in the US National Archives showed most of the works were returned to the collector, Hildebrand Gurlitt.

At least one of the pieces listed in the documents appears to be among the 1,400 works that German authorities said this week they found at the apartment of Gurlitt's son, Cornelius, in Munich last year.

Masurovsky, co-founder of the Holocaust Art Restitution Project, said that he searched the US National Archives online after media reported the Munich find this week.

Masurovsky said he dug up a five-page list of the works from Gurlitt's collection. According to him, about 115 paintings along with other works were inventoried in 1946 by the Monuments, Fine Arts and Archives programme (MFAA). Those in the programme, set up by the Allies in 1943 to protect cultural property, were often known as the "Monuments Men."

Most of the art, which included works by Edgar Degas, Marc Chagall and Max Beckmann, were returned to Hildebrand Gurlitt in 1950 by Theodore Heinrich of the Office of the US High Commissioner for Germany, according to a receipt in the archives.

Masurovsky's group posted the list on his group's Facebook page and publicized the discovery on Twitter on Wednesday.

Four paintings were not returned to Gurlitt, instead going to French authorities in 1947, Masurovsky said.

The National Archives could not immediately confirm the authenticity of the documents on Wednesday.

Officials at the US State Department did not immediately comment.

The works seized by the Allies include a self-portrait by Otto Dix, which was one of the pictures that German authorities said this week was in the trove found in Cornelius Gurlitt's apartment. The German government has not provided a full list of what was found there.

The art works listed by the allies are "a window into what is in the hands of the German authorities," Masurovsky said.

If the United States released the works back to Gurlitt, they may have done so in error, according to Jonathan Petropoulos, a history professor at Claremont McKenna College in California, and author of "The Faustian Bargain: The Art World in Nazi Germany."

"The Monuments Men were not perfect," Petropoulos told Reuters.

Hildebrand Gurlitt was one of four dealers chosen to liquidate "degenerate" art purged from state collections during the Nazi era, Petropoulos said.

Some 300 of the works in the Munich trove were reportedly purged from German state museums, while the rest may have come from victims of the Nazis.

Gurlitt also was a dealer for Hitler and the Fuhrer Museum, Petropoulos said, and may have acquired many of the other 1,200 works from a Nazi art-looting headquarters in Paris.

When he fled to the West after the war, Petropoulos continued, the dealer is reported to have said he lost everything in the bombing of Dresden. He died in 1956.

The Holocaust Art Restitution Project issued a statement on Wednesday saying the governments of France, Belgium and the Netherlands had a legal and moral responsibility to demand the German government release a list of all items seized from Cornelius Gurlitt. It also called for an international commission to be established to help identify the works and objects.