Police have arrested more than 30 people in cities across northern Italy

Police in Italy say they have broken up a drug ring that used a convent outside Milan to smuggle cocaine.

They said the convent's South American caretaker organised religious trips in which smugglers posing as pilgrims hid cocaine in their prayer books.

The nuns were "completely unaware" of what he was up to, police said.

They have arrested 33 suspects and seized 30kg (66lb) of cocaine. They say the mafia and Colombian cartels were allegedly behind the operation.

Police said the operation, in the northern city of Piacenza, had been three years in the making.

The drugs were taken from the convent to a house near Bergamo, where the cocaine was refined, cut and sent off to major cities for distribution, the police said.

Two suspected Milan-based drug-trafficking kingpins from the Calabrian 'Ndrangheta crime syndicate were among those detained, Italy's Ansa news agency reported.