Spanish police on Saturday said they had thwarted a criminal gang that flew helicopters to smuggle hashish into the country from Morocco, in a rare operation against aerial drug trafficking.

The helicopters were capable of transporting between 500 and 900 kilograms of drugs, which were stored in rural estates and warehouses in southern Spain before distribution by road to other European countries, the Civil Guard said in a statement.

Police seized one of the helicopters, 1,448 pounds of hashish, five firearms, cash and vehicles during raids in the provinces of Malaga, Almeria and Murcia.

"The late-night movements of several individuals under investigation between Málaga and Almería raised suspicions among Civil Guard investigators of a possible large-scale drug trafficking operation," the Civil Guard said. "Agents discovered that these movements stemmed from close collaboration with others who were making frequent drug shipments from Morocco."

Six arrests were made in the operation, which also involved Moroccan, Belgian and Swedish law enforcement.

"It is rare for helicopters to be used to smuggle drugs but occasionally they (criminal gangs) do try. Remember that helicopters are easy to detect and hard to buy on the black market," a police source told the Reuters news agency.

Police released several images of the operation, dubbed "Giro," on social media.

The helicopters landed in sparsely populated areas, where several people were waiting to unload the hashish and transport it in vans to various storage facilities, police said.

Spain's close ties with Latin America and proximity to Morocco make it a key entry point for drugs into Europe, but smuggling typically takes place by sea.

Spanish police have in the past year also uncovered networks that used drones to transport drugs from Morocco.

Last month, Spanish police said they broke up the local operations of the Jalisco New Generation Cartel (CJNG), which is designated a terrorist organization by President Trump, making 20 arrests.

In October, Spanish police said they seized 6.5 tons of cocaine and arrested nine people after a U.S. tip-off led them to raid a ship off the Canary Islands. The DEA provided key "information" that enabled the operation to succeed, police said.