Around 40 anarchists shouted slogans against Italy's tough 41 bis prison regime and in solidarity with jailed hunger-striking anarchist leader Alfredo Cospito, followed by police in riot gear.
About 700 police officers were deployed in the lagoon city from early morning in readiness for the protest, which had been organised in solidarity with Juan Antonio Sorreche Fernandez, a 45-year-old Spanish anarchist sentenced at first instance to 28 years by the Court of Treviso for the 2018 bombing of K3, the right-wing League party's headquarters in Villorba.
Milan prosecutors told surveillance court judges on Friday that they were not in favour of allowing Cospito to serve his sentence under house arrest.
The 55-year-old is asking for his 30-year jail term to be commuted to house arrest on health grounds.
The hearing took place in the penitentiary ward of the San Paolo hospital in Milan, where Cospito is receiving medical treatment made necessary by his five-month hunger strike.
The anarchist leader has now stopped taking supplements and ingests only water with salt or sugar.
On Wednesday last week he suffered transient cardiac arrest.
ANSA