The Santiago Maldonado cell of the Informal Anarchist Federation (FAI) and the International Revolutionary Front (FRI) claimed to have executed the attack.
The reliability of the claim is being assessed by investigators.
No one was hurt in the blast, which occurred on Via Britanni in Italy’s capital.
The device consisted of a metal container holding gunpowder and a fuse and featuring a timer.
It was said to resemble an explosive device that went off in a Rome post-office car park in May.
Two hooded persons placed the makeshift bomb in front of the police station before fleeing, police said.
There were about 10 people inside the station at the time.
Carabinieri Commander in Chief Tullio Del Sette said Italian police will not be “intimidated” by such acts.
“Instead, they will continue with renewed commitment their daily activity in the service of the country and its people,” he added.
With ANSA
