Anti-immigrant Salvini, who is also deputy prime minister and a big user of social media, tweeted about a swoop on the Italian Mafia in Sicily and immediately afterwards about the "arrest in Turin of 15 other Nigerian mafia members".

However, the chief prosecutor in the northern city, Armando Spataro, said in a statement that while there were 15 arrest warrants, they were not all for mafia-related crimes and, most notably, not all the suspects had yet been arrested.

Some of the suspects were "still being sought", Spataro said, noting that police usually wait for a prosecutor's green light before releasing operational details.

"In the future it would be better if the minister of the interior avoids making similar statements, or at least checks to avoid any risk of harming ongoing investigations," Spataro said.

Salvini swiftly retaliated with his own statement that it is "unacceptable to say that the interior minister could harm investigations and jeopardise arrests".

"If the police chief writes to me at 7:22 am informing me of operations against the mafia and organised crime, as he does regularly, I feel free and honoured to thank and congratulate the police."

Salvini wished Spataro "a very peaceful retirement in the future".