Varese police inspector Carla Galluccio said no-one was hurt in the explosions in front of the HQ of the Northern League, an anti-immigrant party. She said anarchists were believed to be responsible.
An Italian anarchist group has claimed responsibility for sending three letter bombs to embassies in Rome in the past week which wounded two people.
It was not known if the attacks were linked.
The Northern League - whose founder, Umberto Bossi, lives close to the party headquarters in Gemonio - once advocated secession for Italy's prosperous north.