A Brazilian museum robbed of valuable artworks has put up a reward of $5,000 (£2,876) for their safe return.
The robbers disappeared among Carnival revellers
The Picasso, Dali, Matisse and Monet paintings were stolen from the Chacara do Ceu museum in Rio de Janeiro while carnival festivites were in full swing.
A telephone line has also been set up allowing anyone with any information about the theft to call anonymously.
Experts say the artworks, the museum's most valuable pieces, are worth up to $50m (£28.7m).
Police have also issued computer-generated images of the armed thieves and given details of the paintings to 182 countries via Interpol, while Brazilian authorities are on alert to stop the items leaving the country.
At least four men are believed to have been involved in the heist.
The thieves reportedly brandished a hand grenade to threaten security guards at the museum on Friday.
They shut down the security cameras and then slipped away in a crowd of Samba revellers, said museum officials.
Pablo Picasso's The Dance, Salvador Dali's The Two Balconies, Henri Matisse's Luxembourg Gardens and Claude Monet's Marine were stolen.
"They took advantage of a carnival parade passing by the museum and disappeared into the crowd," said museum director Vera de Alencar.
She said the robbery appeared to have been masterminded by specialists, probably from international gangs.
A number of tourists who were visiting the museum at the time were also mugged by the gang.