Spanish police seized 11 metric tons (12.1 U.S. tons) of hashish smuggled from Morocco on trucks with fuel tanks rigged to hide the drugs and arrested 35 people in what was described as the breakup of a major smuggling ring feeding the European market, authorities said Wednesday.

Much of the haul was displayed across a patio outside the headquarters of the National Police, with some hashish packaged in small amounts resembling bars of soap, while much of it was held in suitcases made out of tape and packaging material.

Authorities said the hashish traveled in trucks that took cargo ferries from Morocco to southern Spain, and were then driven to a Madrid suburb where the hashish was extracted from the vehicles' fuel tanks. From there, some of the hashish was sent to Madrid for sale while the rest was put aboard other trucks carrying legal merchandise to countries including Belgium, Britain, France and Holland.

Those arrested included 31 Moroccan nationals, three Spaniards and a Belgian woman. One of the Spaniards and the Belgian woman were truckers driving rigs with loads of carrots and clothing with the hashish hidden amid the legitimate cargo, National Police chief Ignacio Cosido said.

Cosido declined to put a value on the hashish seized except to say "it's very profitable." Police also seized numerous bags of marijuana, (EURO)150,000 ($198,000) in cash, 14 vehicles valued at (EURO)400,000 and 109 cellphones during the course of an eight-month investigation that started when authorities broke up a Madrid hashish selling ring and went after that group's suppliers.

The ring used GPS systems to track the movements of their hashish loads, and the specially designed gas tanks to hold the drugs were put back together again for reuse after being dismantled, said Jose Luis Conde, who heads the National Police's Madrid division.

Conde declined to say whether the hashish originally came from Morocco, a major producer, saying only that it was from North Africa.