The killing of six Africans near Naples was described as "terrorism"
About 30 suspected mobsters have been arrested around Naples in the latest stage of what Italy's interior minister has called a "war" with the mafia.
They include three men believed to be involved in the killing of six African immigrants near Naples on 18 September.
The operations, which involved 500 police officers, targeted the Casalesi clan of the Naples mafia, the Camorra.
Interior Minister Roberto Maroni said: "The war against the Camorra will continue until it is won."
Last week Mr Maroni said the Camorra had declared a "war on the state".
Tuesday's actions were "the state's first big response", he said.
However, the government has already promised tough action, last week announcing the deployment of 500 troops to the southern Campania region around Naples.
They are due to be in position later this week.
Mr Maroni described the killings of an Italian national and the immigrants from Ghana, Liberia and Togo as an "act of terrorism", and said the Italian government "must respond firmly and regain control of the region".
It is thought the killings may have been the Camorra's response to what it saw as foreigners moving in on its drug-trafficking activities.
The three suspects were arrested in small villas on the coast near Naples, the police commander of the operation said.
The raids also uncovered two AK-47 assault rifles - believed to have been used against the Africans - as well as pistols, police outfits and other disguises, Gianfrancesco Siazzu said.
Another man suspected of killing the Africans was arrested last week.
The arrests were part of what is said to be one of the biggest operations against organised crime syndicates in Italy in a decade.
On Tuesday police were acting on 107 arrest warrants.
Many of those targeted were already in prison, but police said this operation would keep them there.
Along with the arrests, the police calculate they have seized assets worth 100m euros (£80m).