(ANSA) - Milan, January 28 - Italian police on Tuesday arrested 18 people on suspicion of tax fraud linked to a chapter of the Calabria-based 'Ndrangheta mafia which has been bedded down in Lombardy for many years.

The arrests were made by some 300 tax police in Lombardy, Piedmont, Lazio, Val d'Aosta and Calabria.

Police seized some 32 million euros in assets.

The tax fraud amounted to over 160 million euros, police said.

In a wiretap in the probe, police overheard one of the bosses saying the gang could make some four million euros a year from waste trafficking and disposal.

'Ndrangheta, Italy's richest and most powerful mafia thanks to its congtrol of the South America-Europe cocaine trade, has long expanded beyond its Calabrian roots to the rest of Italy and most of the rest of the world.

Italian police have gradually been digging behind the wall of silence or omerta' that for 'Ndrangheta is even more impenetrable than that of Sicily's Cosa Nostra.

In January 2015 police arrested more than 160 people in the biggest-ever operation against a northern business arm of 'Ndrangheta.

The op showed how far the one-time southern kidnapping gangs - long poor relations to Sicily's Cosa Nostra but now grown plump on cocaine cash - had infiltrated the economy of Italy's most affluent regions, especially the thriving economy of Reggio Emilia around Bologna.

Other probes have shown 'Ndrangheta infiltration in the region around Milan, Lombardy, the region around Genoa, Liguria, and the region around Turin, Piedmont.

In February 2014 a major Italian-FBI bust showed that 'Ndrangheta was muscling in on the drug operations of one of Cosa Nostra's historic five families in New York, the Gambinos.

Before that, in July 2010, a massive police operation netted the head of the 'Ndrangheta and 300 others.

Domenico Oppedisano, 80, anointed the equivalent of the 'boss of bosses' in Cosa Nostra at a Calabrian shrine to the Madonna a year previously, was caught along with their reputed head in Lombardy, Pino Neri.

'Ndrangheta is so secretive that the replacement for Oppedisano is not known.

'Ndrangheta (from a Greek word meaning 'heroism' or 'virtue') once lived in the twin shadow of Cosa Nostra in Sicily and the Camorra in Naples.

While those two syndicates, notably the Sicilians, were feeding off the transatlantic heroin trade through operations like the infamous 'French connection', 'Ndrangheta was only just emerging from its traditional stock-in-trade of kidnappings in the Calabrian highlands.

It has since become a highly sophisticated global network with a chokehold on the European cocaine trade and control over swathes of its home turf where police fear to tread, Italian officials say.

As well as being the richest, 'Ndrangheta is also regarded as the most impenetrable of Italy's mafias, with its close-knit family-based organisation outdoing the Sicilian mafia in its ability to defeat police efforts to turn members into State witnesses.

The European law enforcement agency Europol has identified the 'Ndrangheta mafia as one of the "most threatening" organized crime groups on the global level, due to its "enormous financial might" and "immense corruptive power," with a presence in Germany, Spain, the Netherlands, France, Belgium, Switzerland, Canada, US, Colombia and Australia, where 'Ndrangheta turf wars have gained headlines.

In Europe, 'Ndrangheta really only came into the public eye in 2007, when six clan members were gunned down on the midsummer Ferragosto holiday in the German city of Duisburg in a feud that began as a wedding spat in 1991.

A string of 'Ndrangheta-linked businesses have been seized in the last few years all over northern Italy, and especially in the affluent Lombard belt around Milan, and a Lombardy regional councillor was placed under investigation for buying votes from transplanted clans.

On the Italian Riviera, the town councils of Bordighera and Ventimiglia were dissolved for 'Ndrangheta infiltration in 2011 and 2012, the first non-Calabrian municipalities to be wound up because of such penetration.

In Rome, the Calabrian Mob has laundered money in a string of plum properties, as attested to by recent seizures police say are only the tip of the iceberg.

In November 2013 Grand Hotel Gianicolo, a former monastery converted into a four-star hotel for the Catholic Church's Jubilee in 2000, was seized from Calabrian businessmen linked to the 'Ndrangheta.

It is one of the swankiest properties on the hill, Gianicolo or Janiculum, that affords one of the most breathtaking views over Rome.

Nine years ago a former Dolce Vita-era bar and restaurant on the storied Via Veneto, the Caffe' De Paris, turned out to be in the hands of the Calabrian Mob.

More recently, gangsters involved in a hitherto-unknown Rome crime organisation that allegedly had fingers in a web of business and political operations were said to have links to other mafias including 'Ndrangheta.

Cosa Nostra, meanwhile, had been reorganising under a new cupola formed since the death in prison of Totò 'the Beast' Riina, the man responsible for the 1992 murders of crusading anti-Mafia prosecutors Giovanni Falcone and Paolo Borsellino.

But a recent police operation dismantled the new power structure, police said.

On January 22 police in Sicily acted to execute warrants issued by anti-mafia prosecutors for the detention of seven people accused of being members of the reconstituted cupola of Cosa Nostra bosses.

The attempt to reform the Sicilian Mafia's commission of leading mobsters was discovered in December when 47 people were held in a previous operation.

Among the suspects detained on Tuesday were Leandro Greco, the grandson of Cosa Nostra's 'pope' Michele Greco, and Calogero Lo Piccolo, the son of Salvatore Lo Piccolo, a boss who is serving a life sentence in jail.

The new operation was launched thanks in part to the testimony of two new State witnesses.

