Italian police have arrested 11 people on suspicion of mafia-linked corruption, tax fraud, money laundering and engaging in organized criminal activity during preparations for the Expo 2015 in Milan, officials said Wednesday.

Milan's Prosecutor of the Republic said the operation was significant because it proved the existence of a tight link between the mafia and financial crime.

The Guardia di Finanza, the Italian law enforcement agency tasked with combating financial crimes, carried out the arrests on behalf of the Milan Anti-mafia Directorate (DDA).

The investigation involves Dominus Scarl, a consortium that set up some of the more than 50 pavillions present at the Expo, which was held between May 1 and October 31 last year.

Dominus Scarl allegedly secured contracts for the international trade fair using mafia intermediaries, targeting contracts for pavilions that included those of France, Kuwait and Equatorial Guinea, police said.

A system had allegedly been set up that involved producing false invoices, creating slush funds and transferring money to Sicily, where investigators found ties to the Pietraperzia mafia clan.

Ilda Boccassini, the DDA's coordinator in Milan, pointed out that the investigation showed there are two different organizations operating in the administrative region of Lombardy: the 'Ndrangheta (Calabrian mafia) and the Cosa Nostra (Sicilian mafia).

Guardia di Finanza agents have seized around 5 million euros ($5.5 million) during the operation, according to local media.

Judge Cristina Mannocci issued the arrest warrants after anti-mafia prosecutors Sara Ombra and Paolo Storari greenlit Wednesday's raids.

In the months preceding the Expo's inauguration, Italian media had already reported some allegations and rumors that the mafia had infiltrated the event's contruction works.

In 2014, the Guardia di Finanza arrested seven individuals suspected of being part of a network that was illegally manipulating the Expo's contract bids.

Among those arrested was Angelo Paris, the director of the Expo's construction projects and head of Infrastrutture Lombarde, a real estate company operating in Lombardy.

The company's previous CEO, Antonio Rognoni, as well as former Members of Parliament Gianstefano Frigerio and Primo Greganti, were also among the arrested; the latter two had been previously sentenced in the 1993 "Clean Hands" corruption maxi-trial.