Two police officers were shot and wounded outside the Italian prime minister's office on Sunday as Enrico Letta's new government was being sworn in around a km (mile) away at the president's palace, RAI state television reported.
One man was arrested at the scene of the shooting, a witness said, and it was initially unclear whether the attack was linked to the launch of the new government.
One of the officers was shot in the neck and was in a serious condition, a police official said.
Letta, 46, the moderate deputy head of the Democratic Party (PD), on Saturday ended two months of political stalemate since February's inconclusive election when he brought together former political rivals in a broad coalition government.
Letta's ministers stepped forward one by one to swear allegiance to the republic before President Giorgio Napolitano, who personally picked Letta as prime minister and had a central sole in the choice of his cabinet team.