Spanish police said on Monday they had seized six underwater drones capable of transporting large quantities of drugs from Morocco to Spain and broken up a gang suspected of manufacturing them. 

Officers seized six of the so-called "drone submarines" and arrested eight people in raids carried out in Barcelona and the southern provinces of Malaga and Cadiz, a police statement said.

Police said it was the first time they had seized such devices, which are officially known as unmanned underwater vehicles (UUVs). 

They believe the gang made underwater drones "capable of bearing big loads" for use by other criminal organisations.

"These devices could allow drug traffickers to transport large quantities of narcotics remotely across the Strait of Gibraltar," the statement said. 

The drones had up to 12 motors each and a range of 30 kilometres (18 miles). 

That is easily enough to manage an underwater crossing of the Strait of Gibraltar separating Spain from Morocco which measures just 15 kilometres (nine miles).

Three of the drones were due to be delivered to a French drug ring to "transport significant amounts of cocaine", the statement said.

The gang also built false bottoms into vehicles to allow gangs to smuggle drugs, as well as "unmanned semi-submersible vessels" that could carry up to 200 kilogrammes (440 pounds) of product.

Their customers included criminal gangs in Denmark, France, Italy and Spain, police said.

Spain’s physical proximity to Morocco, a major hashish producer, and its close ties with former colonies in Latin America, a major cocaine-producing region, have made it a key entry point for drugs bound for Europe.