LISBON, Portugal (AP) — Portuguese and Spanish police say they have arrested 15 people on suspicion of trying to smuggle 2.1 metric tons of hashish into Spain hidden inside a concrete mixer truck.

A cross-border investigation that began last year allowed officers to detect the truck, escorted by a van full of suspects, as it entered Portugal from Spain to be loaded up in a secluded location near the town of Tavira.

Police intercepted the truck there and found drugs hidden behind a truck trap door.

Investigators seized 2,140 kilos (4,718 pounds) of drugs and arrested three Spaniards, a Romanian citizen and a Moroccan national, a statement said Saturday.

Spanish police then arrested 10 Spaniards preparing to receive the drugs, including two Spanish police officers, in the southwestern region of Huelva.