Armed, masked thieves burst into a lightly guarded Oslo museum Sunday and snatched the Edvard Munch (search) masterpiece "The Scream" and a second Munch painting from the walls as stunned visitors watched in shock.

It was the second time in a decade that a version of the iconic "Scream," which depicts an anguished, opened-mouthed figure grabbing the sides of its head, had been stolen from an Oslo museum.

The thieves, who fled by car, also grabbed "Madonna," another priceless painting that along with "Scream" is part of Munch's "Frieze of Life" series painted in 1893-94, depicting themes of sickness, death, anxiety and love.

The two or three thieves, wearing black masks, threatened an employee of the Munch Museum (search) with a handgun before grabbing the paintings, easily snapping the wires that attached them to the wall, witnesses and the police told The Associated Press and local media.

Many museum visitors panicked and thought they were being attacked by terrorists.

"He was wearing a black face mask and something that looked like a gun to force a female security guard down on the floor," one witness, Marketa Cajova, told the NTB news agency.

"What's strange is that in this museum, there weren't any means of protection for the paintings, no alarm bell," a French radio producer, Francois Castang, who saw the theft told France Inter radio.

"The paintings were simply attached by wire to the walls," he said. "All you had to do is pull on the painting hard for the cord to break loose -- which is what I saw one of the thieves doing."

A photo taken by a witness outside the museum appears to show three black-clad robbers, two of whom are walking to a small, black getaway car with the paintings in hand. The third robber appears to be opening the trunk. The witness who took the photo did not want to be identified.

Police spokeswoman Hilde Walsoe told AP that no one was injured during the robbery and that police had found the escape car -- an Audi A6 -- and fragments of the paintings' frames.

Munch, (pronounced "moongk") a Norwegian painter and graphic artist who worked in Germany as well as his home country, developed an emotionally charged style of great significance in the birth of the 20th century Expressionist movement (search). He died in 1944 at the age of 81.

The stolen "Madonna" depicts an eroticized virgin with a blood-red halo in a dark, swirling aura. Munch later produced woodcut lithographs of a similar subject.

Munch made four versions of "The Scream," an image that has fascinated experts and the general public for decades. Art historians and amateurs alike have pondered the meaning of the enigmatic, seemingly bleak image, which over the years has found fame in the popular culture in serious reproductions but also cartoons and novelty items.

The Munch Museum had two of the "Scream" pictures; a private collector owns a third version; and the fourth is on display at Oslo's National Gallery. That version was stolen in February 1994 but recovered three months later.

The version stolen Sunday was a tempera painting on board.

"They were all painted by Munch, and they are all just as valuable," Munch Museum spokeswoman Jorunn Christoffersen told AP. "Still, these paintings are not possible to sell, and it is impossible to put a price tag on them."

However, Knut Forsberg, manager of Blomqvist Fine Arts, Norway's oldest auction house since 1870, estimated the value of "The Scream" at between $59.6 million to $74.5 million. But he agreed it would be impossible to sell either painting on the open market because of their notoriety.

"Most likely, the thieves will demand a ransom to deliver the paintings back," he said.

Forsberg also refused to censure the museum for any lack of security.

"You could fasten the picture better, but then the thieves would just cut the picture from the frame and damage the painting," he said.

Christian Gether, curator of the Arken museum of modern art in Ishoej, a Copenhagen suburb, where "The Scream" was on exhibit in 2001, also said he was against having armed guards and metal detectors in museums.

"It is not a pleasant experience to enter a museum where there is a guard at the entrance with gun," he told Denmark's public radio.

The French radio producer said police arrived at the scene after 15 minutes. Visitors were ushered into the museum's cafeteria. But police claimed to have made it there within only a few minutes after they were notified of the theft, at 11:10 a.m. The closest police station is only a half-mile from the museum.

By 1 p.m., police had cordoned off the area around the museum to interview 25 witnesses.

The "Scream" stolen in 1994 was a work on paper. Police recovered the fragile work undamaged in a hotel in Asgardstrand, about 40 miles south of Oslo. Three Norwegians were arrested.

At the time, investigators said the trio tried to ransom the painting, demanding $1 million from the government. It was never paid.