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Police say 75 people have been arrested and more than 3,500 stolen artifacts and pieces of art seized in a vast joint operation involving 18 European countries that dismantled an international cultural goods trafficking ring.

Several of the seized objects "are of great cultural importance in the archaeological world, such as a marble Ottoman tombstone and a post-Byzantine icon depicting Saint George," Europol said in a news release Monday.

Operation Pandora focused on the illicit trafficking of cultural goods, with a particular emphasis on war zones. Europol

Authorities said they had secured up to 500 archaeological objects alone in the southern Spanish town of Murcia, including 19 that were taken from the local archaeological museum in 2014.

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More than 400 coins from different periods were also seized.

The multi-national investigation — named Operation Pandora — started in October and the arrests began in November. It was led by investigators from Spain and Cyprus with support from 16 other countries, UNESCO and Interpol.

It focused on "cultural spoliation" — the act of taking goods by force or looting, particularly in times of war.

Almost 30,000 vehicles and 50 ships were checked by investigated and 48 588 people were checked, Europol said.

It was not clear why the operation's results were announced two months after the arrests.