An explosion injured five people at an election rally in Bologna where the leader of the National Alliance (AN) Mr Gianfranco Fini was addressing a crowd on Tuesday evening, Ansa news agency said.
Ansa said the blast was caused by a "paper bomb".
AN is the second biggest party in the centre-right coalition government. A small bomb damaged one of its offices in Sardinia this week as the party campaigned for European Parliamentary elections this weekend.