Camouflage-clad police backed by helicopters swooped into the southern Italian mountain village of San Luca, the epicentre of a 16-year-old feud inside the Calabrian underworld organisation, the ' Ndrangheta, that has claimed up to 20 lives.

The six men died in a hail of bullets on August 15 outside a pizzeria run by Calabrians in Duisburg, northwest Germany, where the ' Ndrangheta is believed to be well established.

Among the arrested was Giovanni Nirta, the suspected head of a mob clan whose wife was shot dead last Christmas.

Achille Marmo and Giovanni Strangio, brothers of two of the Duisburg victims, were also among those arrested in and around San Luca.

The suspects, some of whom were found hiding in an underground bunker, face charges including association with the mafia, murder and arms trafficking.

"It's still too soon to say if those directly involved in the (Duisburg) massacre are among them," a police spokesman said.

The feud is believed to have its roots in rancour over an egg-throwing incident during Carnival in 1991.

German police, already in Italy following up the Duisburg shootings, flew into the southern city of Reggio Calabria, near San Luca, today.

The Calabrian mafia is estimated by Italian experts to have an annual turnover on a par with some of the largest publicly quoted companies in Italy.

Much of its cash comes from trafficking cocaine, a trade which the ' Ndrangheta now dominates in Italy. It has outgrown other Italian mafias like its more famous Sicilian counterpart, the Neapolitan Camorra, and the Cosa Nostra.