Two blasts on Friday outside a post office in central Rome near the ancient Roman Circus Maximus caused damage to a parked car but no injuries, police said.
District police chief Massimo Improta said explosions in Rome's Piramide district were caused by a "crude" homemade device.
The first blast was probably caused by the device's fuse and the second by a plastic bottle of inflammable liquid, Improta said.
Police described the blasts as a "symbolic" and apparently "limited" act that could not have caused much devastation.
Sniffer dogs and explosives teams were deployed at the scene, which was blocked off with police tape, but did not found any other devices, according to police.
Police said investigators were examining footage from security cameras in the area in a bid to identify those responsible for planting and detonating the devices.
Anarchist groups have previously targeted post offices in Italy but police declined to say if such groups were their main line of inquiry.
