Spanish police have impounded what is believed to be a national record haul of cocaine from a ship in the Atlantic Ocean, with the seizure potentially reaching 40 tons, a union said on Monday.

The Civil Guard intercepted the vessel in international waters off Spain's Canary Islands on Friday, with around 20 people arrested, sources from the force's main AUGC union told the Agence France-Presse.

It is estimated that "between 35 and 40 tons of cocaine have been seized" because the hold "was completely stuffed" with bales of the drug, making it "a historic seizure," the sources said.

The boat, now being inspected in the Canary Islands, had left Sierra Leone's capital Freetown for Benghazi in Libya.

But the pattern of previous such operations suggests it was due to offload the drug onto smaller vessels for distribution in Europe because "the unloading of this volume of cocaine in Libya doesn't make much sense."

"Many vessels would be needed, different ports, because such an unloading in a single port would arouse a lot of suspicion. So the operation is probably coordinated through international networks," the AUGC sources said.

Spain's Interior Minister Fernando Grande-Marlaska told reporters in Madrid, including AFP, that the seizure "was one of the biggest, not only nationally but internationally," without providing further details.

A court order means the investigation is under legal secrecy, the AUGC sources added. The Civil Guard declined to confirm the details of the operation.

Spain's close ties with Latin America and proximity to Morocco, a top cannabis producer, make it a key entry point for drugs into Europe.

In January, police made their biggest seizure of cocaine at sea from a ship that was carrying almost 10 tons of the drug.

Last October, Spanish police 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.

In June 2025, police forces dismantled a drug trafficking ring that used what authorities called high-speed "narco boats" to smuggle large quantities of cocaine from Brazil and Colombia to the Canary Islands. The ring allegedly used an abandoned shipwreck as a refueling platform for the speedboats.

In 2024, Spanish police impounded 13 tons of cocaine from a container ship that had arrived at the southern port of Algeciras from Ecuador, the country's largest-ever haul of the drug.