Some 250 officers in Italy, Spain, Britain and Germany simultaneously swooped on 40 houses – the culmination of a four-year investigation led by the Italians, the European police agency said.

In Italy, the raids were focused on the regions of Sicily, Calabria, Piedmont, Apulia, in what is considered one of the biggest crackdowns in such crimes "in Italian history".

In the Sicilian Caltanissetta area, "which is rich in archaeological sites from the Greek and Roman epochs, local members of the organised crime group illegally excavated artefacts," Europol said.

The items were then smuggled out of Italy, "equipped with false provenances and sold via German auction houses."

Facilitators in Barcelona and London helped organise the "supply chain" and provided technical support.

Police also seized 1,500 tools including metal detectors in the early morning raids.

"International cooperation is key to the success of such investigations in the field of trafficking of cultural goods, in which artefacts are moved through several EU countries and levels before they are brought to the legal market," Europol added.