German and Italian police Tuesday arrested four men for the August slaying of six Calabrians, who were gunned down outside a Duisburg, Germany, pizzeria.

''With these arrests the offensive against the Calabrian mafia is reaching its peak,'' Italy's Interior Minister Giuliano Amato told ANSA.

The feud between warring clans in the Ndrangheta, the equivalent of Sicily's Cosa Nostra, has killed up to 20 people, and began during a 1991 carnival celebration over an egg-throwing incident.