Two police officers were shot and wounded as the new Italian government was being sworn in.
The two men are members of Italy’s national military police known as carabinieri.
A man was arrested at the scene. He is being named as Luigi Preiti – a man in his forties, from the southern Italian region of Calabria.
The carabinieri were attacked outside the office of the country’s new prime minister Enrico Letta – less than one kilometre from where his government was being sworn in at the presidential palace in Rome.
One of the officers is said to be in a serious condition with a gunshot wound to the neck. The other is believed to have been shot in the leg.
Home Affairs Minister Angelino Alfano and Defence Minister Mario Mauro visited the carabinieri in hospital.
Reports in Italian press say the man arrested fired at least six shots before being tackled by other officers. He is said to be unemployed and it is believed that he travelled to Rome by train.
There is no information about the motive for the attack, but it comes at a time when Italy is facing bitter political division and a long economic slump.