The agency said the drugs were found in a shipment of legally imported whole frozen tuna that had arrived from Ecuador. Officers used chainsaws and shovels to open the carcasses and remove the blocks of cocaine hidden inside.

“At least 500kg of narcotics concealed in legally imported frozen whole, uncleaned tuna carcasses were discovered and confiscated in a cargo container arriving from Ecuador,” the FSB said. Photographs released by the agency showed rows of fish alongside more than 100 bricks of cocaine.

The FSB said it had “foiled the illegal activities of a Russian citizen involved in organising an international smuggling network” moving large cocaine shipments from Latin America by sea. A suspect has been detained and a criminal investigation into attempted drug trafficking is under way.

Russian media reported that officers seized cryptocurrency wallets, luxury watches and vehicles during searches linked to the case.

Authorities say Russia has increasingly become a transit route for Latin American cocaine, with smugglers using a range of concealment methods including fruit shipments, coffee and seafood.