"The armed robbers had hidden inside the post office. They jumped out at the staff on their arrival and forced them to open up the vault," said a policewoman in charge of the probe into the theft in the Italian city.
Some €50,000 in cash and €20,000 in tax stamps were stolen by the thieves, who fled back along the 12-metre (39 foot) long tunnel which they are believed to have dug during the weekend, she said.
Before making their escape, the bandits - dressed entirely in black - locked the 12 members of staff in the vault. Their toy guns were later discovered discarded in the tunnel.