AMSTERDAM (AFP).- Amsterdam's Van Gogh Museum on Monday unveiled a newly discovered landscape painting from the height of the Dutch master's career, abandoned for years as a forgery in a Norwegian attic.

"Sunset at Montmajour," a large oil landscape from 1888, was unveiled to applause by the museum's director Axel Rueger as a "unique experience that has not happened in the history of the Van Gogh Museum."

Depicting a landscape of oaks in the south of France, the painting was brought to the museum from a private collection.

Researchers set to work and authenticated it based on comparisons with Van Gogh's techniques, style, paint used and a letter he wrote on July 4 1888 in which he described the painting.

It had been lying for years in the attic of a Norwegian collector who thought the painting was a forgery, after buying it in 1908.

"This discovery is more or less a once in a lifetime experience," said researcher Louis van Tilborgh, who helped with its authentication.

"All research indicates that this is a painting by Van Gogh," he added.

The long-lost painting was made at around the same time as some of Van Gogh's most famous works, including "Sunflowers" and "The Bedroom".

"This is a very, very special morning and you're seeing a very, very happy director in front of you," Rueger told AFP.

"When I was told that it had been authenticated as a genuine Van Gogh I could not believe it."

The museum declined to be drawn on the identity of the mystery collectors.

"Unfortunately we cannot divulge too much about the identity of this collector as we need also to protect his privacy," Rueger said.

"But what I can tell you is that the painting has been lying in the attic for most of this time."

Rueger admitted that the museum had previously been approached by the collector "but we did not have the technology at the time to authenticate the painting."

The Van Gogh Museum reopened its doors to the public in early May with a stunning new display of some of the Dutch master's greatest works, completing a trio of renovations of the city's most famous museums.

It is located on Amsterdam's historic Museumplein where many other Dutch art treasures like Rembrandt's "Night Watch" can also be found at the recently reopened Rijksmuseum.

The museum features 200 works, 140 by the Dutch master himself and the rest by contemporary painters.

They include other iconic works such as "The bedroom", the "Irises", "The Potato Eaters" and the ominous "Wheatfield with crows."

The newly unveiled Van Gogh will go on display on September 24, on a year-long loan from its owner.

With its reopening, the museum expects to attract some 1.2 million visitors over the next year and is one of the world's 25 most popular museums, according to the City of Amsterdam.

The Van Gogh Museum was the last of Amsterdam's three major museums to reopen its doors after extensive refurbishments, underlining the Dutch capital's status as a top art destination.