Paris, France (CNN) -- Interpol has issued a global alert for a Picasso painting and four other works stolen from a Paris art museum -- a sign that authorities believe thieves may have taken the paintings outside the country.
"These extraordinary paintings by these great masters are so recognizable that they will be difficult to sell in any market," Jean-Michel Louboutin, Interpol's executive director of police services, said in a statement released by the agency Saturday.
Prosecutors estimate that the oil paintings nabbed in a heist at the Modern Art Museum in Paris early Thursday morning could be worth 500 million euros ($617 million). In addition to Picasso's cubist "Pigeon with Green Peas," authorities said works by Henri Matisse, Georges Braque, Amedeo Modigliani and Fernand Leger were also stolen from the city-run museum.
Interpol said it had sent images of the paintings to police in 188 countries and also added them to the agency's online database of stolen artwork.
Christopher Girard, an aide to the mayor of Paris who oversees cultural affairs, said whoever stole the paintings entered through a window and was able to thwart guards and video surveillance. The heist showed signs of organized crime, he said.
"We are dealing with an extreme level of sophistication," he said in a statement posted on the museum's website.
Girard estimated the artwork was worth about 100 million euros ($123.7 million).
Paris Mayor Bertrand Delanoe said in a statement that part of the museum's security system -- the part that detects movement and body heat -- had been broken at least since March 30.
The museum notified the service provider that day and asked for replacement equipment, but it still has not been provided, the mayor said.
Video surveillance of the museum was working normally, and three guards were on duty, he said.
Delanoe called for an administrative investigation in addition to the criminal one to determine if "technical or human failures helped make this security breach possible."
The city completed a 15 million euro ($18.7 million) upgrade of the museum's security system in 2006, he said.
Interpol lists the five stolen paintings as Picasso's "Pigeon with Green Peas" (1911), Matisse's "Pastoral" (1906), Braque's "Olive Tree near l'Estaque" (1906), Modigliani's "Woman with Fan" (1919) and Leger's "Still LIfe with Candlestick" (1922).