MARSEILLE--French police have arrested a night watchman at a museum from where a valuable painting by 19th century artist Edgar Degas was stolen, a judicial official said Friday.

Police in the southern port city of Marseille arrested the man on Thursday, the official said, adding: "It is an employee of the museum, a night watchman."

The colorful image of singers performing on a theatre stage was missing when staff opened up the Cantini Museum in Marseille on Thursday.

The national museums service said the picture was a pastel work titled "The Chorus", worth 800,000 euros (1.14 million dollars).

Loaned by the Orsay museum in Paris for an exhibition of theatre-themed artworks including some 20 works by Degas, it measures 32 centimeters by 27 (about 13 inches by 10).

Prosecutor Jacques Dallest said on Thursday that the painting had been unscrewed from the wall, there was no sign of a break-in and the theft may have been an inside job.

The city hall, which runs the museum, said 70,000 people had visited the exhibition and the show was due to close in Marseille on January 3 and later go on tour to Italy and Canada.