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

A police statement said the three masked men wearing dark clothing entered the museum a half-hour before closing Sunday. 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.

The men were about 1.75m tall 175 cm (and one of them spoke German with a Slavic accent, the 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 100,000 francs (S$128 billion) was offered for information leading to the recovery of the paintings.

The FBI estimates the market for stolen art at US$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.

The four stolen paintings are: 'Poppies near Vetheuil' by Claude Monet (1879), 'Count Lepic and his Daughters' by Edgar Degas (1871), 'Chestnut in Bloom' by Vincent Van Gogh (1890) and 'Boy in a Red Jacket' by Paul Cezanne (1888), police said.

That district is home to the Emil Buehrle Foundation, a private collection founded by a Zurich industrialist which boasts many Impressionist works.

'French Impressionism and Post-Impressionism constitute the core of the collection,' the museum's website says. The foundation was unavailable for comment on Monday. -- AFP, AP