Fierce clashes between police and masked protestors in Naples triggered a row over whether the Italian city's leftist mayor had encouraged activists bent on preventing a rightwing rival from speaking there.
A debate that exposes several faultlines in national politics followed running battles on Saturday involving a small group that broke away from a protest by several hundred people marching against Northern League leader Matteo Salvini.
They began hurling stones, flares, smoke bombs and Molotov cocktails at riot police, who replied with baton-and-shield charges and tear gas.
The confrontation continued for over an hour with a handful of cars vandalised and several rubbish carts overturned.
Police made three arrests and were looking for three other people reported to have been involved. There were no reports of serious injury.
Salvini, an anti-immigration, anti-euro populist who attracts protests whenever he ventures out of his northern stronghold, said he would be filing a defamation suit against the mayor, Luigi de Magistris.
In the run-up to Saturday's clashes, the independent left-winger had branded Salvini a fascist xenophobe with contempt for southern Italy.
He also tried to use his mayoral powers to deny the far right leader a venue for his first rally in Naples.
He was overruled by the local prefect, acting on the orders of the interior ministry.
"De Magistris should resign instead of accusing me of being a Nazi-fascist," Salvini said Sunday.
"Nothing like this has ever been seen in Naples and the worst thing about it is the mayor's support for it."
"Handing Salvini the stamp of being the defender of free speech and the right of political leaders to voice their opinions was, frankly, an unthinkable short-circuit," Francesco Casavola, the former president of Italy's Constitutional Court, told La Repubblica.
De Magistris, who had voiced support for the anti-Salvini protestors earlier in the week, said he did not condone what happened on Saturday afternoon.
"As a former magistrate who is proud of the his city, I distance myself from any form of violence," he said.
Media reports said the protestors involved in the violence were a mixture of militants of the anti-globalisation Black Bloc group and hooligan fans of local football club Napoli, known as "ultras".