Emanuele Pozzolo, a lawmaker for Meloni's far-right Brothers of Italy party, has admitted owning the mini revolver but says he did not fire it.

Prosecutors said in a statement they were looking into possible offences including involuntary or negligent injury and failure to safeguard a weapon. They said they had seized the gun, a North American Arms 0.22 handgun.

They also seized the bullet discharged into the left thigh of a guest, reported to be the son-in-law of a bodyguard of junior justice minister Andrea Delmastro, who newspapers said also attended the party.

The victim has already been discharged from hospital and had not made any formal complaint, the prosecutors said.

"I confirm that the shot was accidentally fired from a pistol I legally held but it was not me that fired," Pozzolo, 38, said in a statement cited by the La Repubblica daily.

Opposition politicians expressed astonishment and outrage at the incident at a party in Rosazza near Turin.

Possession of firearms in Italy is strictly regulated, although Meloni's party last month proposed to reduce to 16 the minimum age for obtaining a permit for a hunting rifle.

"We could not have imagined that the passion for weapons of Giorgia Meloni's party was such that MPs would take them loaded to New Year's Eve parties," said Elly Schlein, leader of the centre-left Democratic Party.

Former centrist prime minister Matteo Renzi added: "Why bring guns to a New Year's Eve party in the presence of MPs and members of the government?

"Meloni's (party) are not a ruling class. They are inadequate, incapable, unpresentable. And dangerous, first and foremost for themselves."

Neither Meloni nor her party has yet to react officially.