Police in Rome say an explosion outside a post office appears to have been caused by a rudimentary explosive device placed between two parked cars.
The blast Friday morning during business hours in the parking area near a side entrance to the post office caused no injuries but damaged a vehicle.
The explosion nwas caused by a "makeshift bomb" planted in the office's car park, Italian police report in a statement.
The post office serves the residential Testaccio neighborhood and is near the foot of the Aventine Hill.
Similar explosions in the past in Italian cities have been frequently blamed on anarchists.
Information service Luceverde, run by the Italian Automobile Club in collaboration with city police, said on Twitter that "technical checks" were being carried out near the post office.
There was no immediate claim of responsibility.