ROME (AP) — A rudimentary explosive device exploded between parked vehicles outside a post office in Rome on Friday, causing no injuries but damaging a car, police said.

A preliminary investigation indicated that the blast likely was "a demonstrative act, showing that it could be done," but apparently not designed to cause major damage, Rome police official Massimo Improta told reporters.

Similar explosions in Rome and other Italian cities in recent years have frequently been blamed on or claimed by anarchists. There was no immediate claim of responsibility.

The post office, an imposing, 1930s Fascist-era building that is often studied by architecture students, remained opened throughout the incident.

The blast occurred in a small parking area outside a side entrance where people go to pick up packages that the post office couldn't deliver because no one was home.

Improta said that a trigger, set off by a timer, initiated the explosion, which then ignited gasoline inside a plastic container that was part of the device, a noisy sequence leading some people at first to think there were two explosions.

The post office serves the residential Testaccio neighborhood and is near the foot of the Aventine Hill.