A suspected bomb was found in an empty underground train carriage in Rome on Tuesday, but police said it lacked a detonator and could not have exploded.
The device, described by one police source as rudimentary, was found by a driver preparing a train for service in a marshalling yard near the Rebibbia metro station at about 0900 GMT, transport authority ATAC said.
It was in a box with cables, batteries and antennas, an ATAC spokesman said.
"It didn't have a detonator, it couldn't explode," a spokesman for the Carabinieri, Italy's paramilitary police force, told Reuters by telephone.
He said it contained a small quantity of explosive powder.
The device was discovered at a time of increased tension in Italy following anti-government protests last week that descended into some of the worst violence in Rome for years.
A senior Iraqi official said last week that al Qaeda was planning attacks in the United States, Britain and Europe around Christmas.
A suspected suicide bomber was killed in a botched attack in Stockholm on Dec 11. Police believe he was planning to attack a train station or department store at the height of the Christmas shopping season.