With the help of Europe's police agency Europol, information from French customs and air support from Italian police, Spanish forces intercepted the boat registered under the Panamanian flag off Spain's southeastern coast on September 23rd.
They said all crew members were detained - 11 Ukrainians and one Uzbek - in what a spokesman for French customs said was "one of the biggest seizures of hashish" ever in Europe.
Hashish seized on a ship off the coast of Spain. Photo: Guardia Civil
The Guardia Civil police force said the boat was intercepted as part of an operation launched in 2013 by Spanish, Moroccan, French, Italian and Greek authorities, with additional support from the US Drug Enforcement Agency.
Some 100 tonnes of hashish have been seized in the multi-country operation and 109 people detained -- with a majority being nationals of Syrian, Moroccan and Spanish.
"This trafficking is being used to finance insurgents in existing conflicts in North Africa and the Middle East," Javier Rogero, lieutenant colonel at the Guardia Civil, told reporters.
He would not be drawn on which groups the drugs and weapons were benefiting, but said police were "convinced... that they also finance jihadist terrorism."
Captagon pills seized
Rogero described the Mediterranean Sea as "a sort of highway for illicit trafficking."
A total of seven boats have been caught as part of the operation - two of them carrying weapons and five full of hashish, believed to be used to buy arms.
The boats had all departed from Turkey. In the case of those carrying drugs, though, the hashish - which came from Morocco - was loaded on board in the Atlantic ocean.
In the case of the two boats carrying weapons, the arms were already on board when they left Turkey.
One of them was intercepted last year, and another in February.
Altogether, they carried 11,400 long guns, more than a million cartridges and ten tonnes of ammonium nitrate, which can be used to make explosives.
One of the boats, which was registered in Togo, was heading to Misrata on Libya's northwestern coast.
The intended recipients are unclear but Misrata is home to powerful militias who were among the forces that seized the capital Tripoli in 2014 and forced the government to flee further east.
But they are now fighting alongside forces from a UN-backed unity government formed earlier this year - and re-established in Tripoli - to oust the Islamic State group from nearby Sirte.
Rogero said that the exchange of information with other countries also allowed the Egyptian navy to intercept a shipment of 1.2 million Captagon pills, an amphetamine popular in Gulf and other Middle Eastern countries that is also believed to play a crucial part in Syria's civil war.
The production of this synthetic stimulant provides income for the warring factions and also keeps fighters awake and energised over long periods.