Italy has long sought the extradition of dozens of leftist guerrillas, who had been given refuge in France on condition they renounced violence following the so-called Years of Lead from the late 1960s to the 1980s.

The period saw hundreds of people killed in violent campaigns by both far-left and far-right groups.

French President Emmanuel Macron's office said the arrests followed months of discussions between Italy and France, with police targeting those militants guilty of "bloody crimes".

Italian Prime Minister Mario Draghi, who took office in February and has established a close working relationship with Macron, welcomed the French action.

"The memory of those barbaric acts is alive in the Italian conscience," his office said in a statement.

An adviser to Macron said the move was made possible by the renewed "climate of trust" between Macron and Draghi, after years of tension between Paris and Rome, particularly when Italy was headed by a populist coalition.

"It was a way for us to show responsibility, recognise this part of Italian history and stop turning a blind eye to the violent acts perpetrated between the mid-60s and the 80s," Macron's adviser said.

French justice minister Eric Dupond-Moretti said he was "proud to participate to this decision that I hope will allow Italy to turn after 40 years a bloody and tearful page of its history."

Amongst those captured was Giorgio Pietrostefani, a co-founder of the Lotta Continua (Continuous Struggle) group, sentenced to 22 years in prison for his role in the 1972 murder of Milan police commissioner Luigi Calabresi.

The other six were members of the Red Brigades, including Marina Petrella, Roberta Cappelli and Sergio Tornaghi, all sentenced to life in prison for taking part in various murders and kidnappings, police said.

A search was under way for three other Italians, Macron's office said, adding that Rome had originally put forward the names of 200 wanted individuals. The Paris prosecutor's office said they would examine any request from Italy for extradition.

Hundreds of people were murdered in bombings, assassinations and street warfare by rival far-right and far-left factions during years of social and political turmoil that petered out as prosecutors gradually uncovered many of the perpetrators.

Numerous leftist militants fled to France, where Socialist President Francois Mitterrand pursued a policy of granting asylum to those who eschewed bloodshed.

Later French governments abandoned that policy, but Italy nonetheless struggled to convince Paris to hand over even those convicted of murder.

In 2008, then-President Nicolas Sarkozy refused to extradite Petrella, citing humanitarian reasons and sparking fury in Italy. Amongst her various convictions, Petrella was found guilty of murdering General Enrico Galvaligi in 1980, as well as two police bodyguards.

Italy's biggest breakthrough in its efforts to bring fugitive militants to justice came two years ago, when Brazil extradited Cesare Battisti, convicted in 1990 in absentia for four murders.

Battisti originally made his home in France, but fled to Mexico and then Brazil when attitudes in Paris started to change.

Australian Associated Press