Six men have been arrested after Dutch police discovered a torture chamber containing a dentist's chair, handcuffs, and tools.
The makeshift prison had been created by converting seven soundproofed shipping containers at a warehouse in the small village of Wouwse Plantage, near the border with Belgium.
When Dutch police searched the containers they found bags containing hedge cutters, scalpels and pliers, tools that officers said were "likely intended to torture victims or at least put them under pressure".
Police had been tipped off by messages on EncroChat , an encrypted platform where users could speak privately between specially-designed handsets.
The platform was used by criminals, recently decoded by French police and shared via Europol.
It is thought there were 60,000 EncroChat users internationally, including 10,000 in the UK, with prices set at Â£1,500 for a six-month contract.
The investigation has already resulted in the seizure of thousands of kilograms of drugs and dozens of firearms by police in the Netherlands and in the UK .
Dutch police found messages on the phones which included photos of the torture chamber - described as a "treatment room" - and the identities of potential victims.
The torture chamber was raided in June, Dutch police said on Tuesday, adding that it had not been used and potential victims had been warned and had gone into hiding.
Dutch police had also searched other properties, including a criminal base near the city of Rotterdam, and found police uniforms, stolen vehicles, firearms and drugs.
Andy Kraag, head of the Dutch National Investigation Service, said the police operation had "prevented a number of violent crimes".
He said the investigation had given a "great result", adding: "Take it from me, many more results will follow".