Rome police have arrested 12 people - including two leaders of a far-right party - after protests against coronavirus restrictions turned into serious riots, Italian media reported on Sunday.
The leaders of Forza Nuova, Giuliano Castellino and Roberto Fiore, were present during the violence in the Italian capital on Saturday after tens of thousands had taken part in an authorized march.
Police, who were involved in several clashes with demonstrators and were pelted with firecrackers, are also checking video footage to see who else should be detained.
About 30 people attacked the emergency room of a hospital late on Saturday where one of the arrested protesters was being treated for an injury.
The rioters broke down the door and clashed with police as well as ambulance workers, the ANSA news agency reported. Four people were injured, including a nurse who took a bottle to the head.
According to media reports, some rioters tried to advance on the official residence of Prime Minister Mario Draghi, but were stopped by police water cannons. Authorities also used tear gas.
The headquarters of Italy's largest trade union CGIL was also stormed and three police officers were injured. Footage on social media showed rioters attacking officers with sticks and flagpoles.
Politicians have reacted with shock. Violent protests are rare in Italy.
The country was the first in Europe to be badly hit by the pandemic in March last year but has managed the health crisis comparatively well since.
New measures against Covid-19 will come into force next Friday.
Every employee in the private or public sector must have a so-called "green pass," which shows proof of vaccination, recovery from or a negative test for Covid-19.
Critics have been campaigning against the measure, which is being introduced to allow further Covid-19 relaxations. Cinemas, theatres and concert halls will be allowed to operate at 100 per cent capacity again if visitors have a green pass.
The attack on the union headquarters follows its support for the measure.
CGIL leader Maurizio Landini spoke of an act of "fascist violence" and an "attack on the constitution."