MILAN (Reuters) - Italy has arrested 11 people accused of crimes linked to public events, including last year's Milan Expo, and channeling money they collected to the Sicilian mafia, police said in a statement on Wednesday.

Seven people were placed in custody and four others put under house arrest on suspicion of money laundering, tax fraud and conspiring to aid a mafia criminal group.

A corruption investigation led to the arrest of several top Expo officials in 2014, blighting preparations for the world fair. Milan prosecutor Ilda Bocassini said in the current case neither event manager Fiera Milano nor the Expo itself were accused of any crime.

Mafia investigations in northern Italy show how criminal groups have spread from their traditional southern fiefdoms and infiltrated legitimate businesses in the wealthier north.

Police accuse the gang arrested on Wednesday of issuing fake receipts for work that was never carried out, avoiding taxes and laundering money, partly through accounts based abroad.

The prime suspect is the de facto boss of several companies that set up fairs and trade shows, including one that worked on the Expo site, police said.

He had close links with a member of the Pietraperzia crime family in western Sicily, who was also arrested on suspicion of facilitating money laundering.

The gang collected cash in undeclared "black funds", and police caught one of the suspects, a lawyer for the Pietraperzia family, trying to take 700,000 euros ($775,460) to Sicily.

Around 5 million euros worth of assets and two real estate properties in Sicily and the Lombardy region around Milan were seized in the investigation.

The arrests on Wednesday are the latest high-profile episode of graft in Italy. On Monday 24 people were arrested in Rome in an investigation of tax fraud and other financial crimes that involved a lawmaker from Prime Minister Matteo Renzi's ruling coalition.

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(Reporting by Isla Binnie)