ZURICH, Switzerland — Three armed men in ski masks stole four paintings by Cezanne, Degas, van Gogh and Monet worth $163.2 million from a Zurich museum in one of Europe's largest ever art heists, police said Monday.

The robbers, who were still at large, stole the paintings Sunday from the E.G. Buehrle Collection, one of Europe's finest private museums for Impressionist and post-Impressionist art, police said.

It was the largest art robbery in Switzerland's history and one of the biggest ever in Europe, said Marco Cortese, spokesman for the Zurich police. He compared it to the theft in 2004 of Edvard Munch's "The Scream" and "Madonna" from the Munch Museum in Norway.

The three masked men wearing dark clothing entered the museum a half-hour before closing Sunday, police said. While one of the men used a pistol to force museum personnel to the floor, the two others went into the exhibition hall and collected the four paintings.

One of the men spoke German with a Slavic accent, police said. They loaded the paintings into a white vehicle parked in front of the museum.

Police, asking for witnesses to come forward, said it was possible that the paintings were partly sticking out of the van as the robbers made their getaway.

A reward of about $90,000 was offered for information leading to the recovery of the paintings _ Claude Monet's "Poppy field at Vetheuil," Edgar Degas' "Ludovic Lepic and his Daughter," Vincent van Gogh's "Blooming Chestnut Branches," and Paul Cezanne's "Boy in the Red Waistcoat."

The FBI estimates the market for stolen art at $6 billion annually, and Interpol has about 30,000 pieces of stolen art in its database. While only a fraction of the stolen art is ever found, the theft of iconic objects, especially by force, is rarer because of the intense police work that follows and because the works are so difficult to sell.

Buehrle, a German-born industrialist who provided arms to the Third Reich during World War II, amassed one of Europe's greatest private collections in the aftermath of the war. He also owned at least 13 works of art at the war's end that were included on British specialist Douglas Cooper's "looted art list," which was used to recover pieces stolen from Jews by the Nazis.

The museum is housed in a villa adjoining Buehrle's former home, which he used to store part of his collection before his death in 1956.

Lukas Gloor, the museum's director, said the robbers stole four of the collection's most important paintings. But, he said, they appeared to have taken the first four they came to, leaving even more valuable paintings hanging in the same room.

The museum also owns Auguste Renoir's "Little Irene" and Edgar Degas' "Little Dancer."

"We are happy that no employees or visitors were hurt," Gloor said.

The stolen paintings were hung behind glass, and a security alarm went off as soon as they were touched, Gloor said at a news conference.

Three other versions of the Cezanne painting _ perhaps the most famous of those stolen _ exist in museums in the United States.

Switzerland boasts a large number of outstanding art collections, some of which have been hit by thefts and robberies over the years.

Last week, Swiss police reported that two Pablo Picasso paintings were stolen from an exhibition near Zurich. The two oil paintings, "Tete de cheval" ("Head of horse") and Verre et pichet ("Glass and pitcher"), were on loan from the Sprengel Museum in Hannover, Germany.

At the end of the 1980s, three armed men made off with 21 Renaissance paintings worth hundreds of millions of dollars from a Zurich art gallery. Stolen works included some by Jan Mertens the younger, Jan Steen, Willem van Aelst and Dirk Hals. The case was made public in 1989 when FBI agents in New York arrested two Belgians and recovered stolen paintings.

In 1994, seven Picasso paintings worth an estimated $44 million were stolen from a Zurich gallery. They were recovered in 2000. A Swiss man and two Italians were jailed for the theft. The stolen paintings included Picasso's "Seated Woman," and "Christ of Montmartre." The two pictures had been stolen from the gallery once before, in 1991.

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On the Net:

E.G. Buehrle Collection: http://www.buehrle.ch/?langen

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Associated Press writers Bradley S. Klapper and Alexander G. Higgins in Geneva contributed to this report.