Dutch police have arrested six men after discovering sea containers that had been converted into a makeshift prison and sound-proofed “torture chamber” complete with a dentist’s chair, tools including pliers and scalpels and handcuffs, a high-ranking officer announced.

Authorities said police conducted the raid before the converted containers could be used and alerted potential victims, who went into hiding.

The discovery was made last month by officers investigating leads generated by data from encrypted phones used by criminals that were cracked recently by French police. Detectives in the UK and the Netherlands have arrested hundreds of suspects based on the encrypted messages.

Tuesday’s announcement gave a chilling insight into the increasingly violent Dutch criminal underworld, which is involved in the large-scale production and trafficking of drugs.

Dutch police said last week their investigations, codenamed 26Lemont, based on millions of messages from the EncroChat phones, had led to the arrest of more than 100 suspects and the seizure of more than 8,000kg (17,600lbs) of cocaine and 1,200kg (2,600 lbs) of crystal meth, as well as the dismantling of 19 synthetic drugs labs and seizure of dozens of firearms.

On 22 June, Dutch national police force officers arrested six men on suspicion of crimes including preparing kidnappings and serious assault. Detectives also discovered the seven converted sea containers in a warehouse in Wouwse Plantage, a village in the south-west of the country, close to the border with Belgium.

They were tipped off by messages from an EncroChat phone that included photos of the containers and dentist’s chair with belts attached to the arm and foot supports. The messages called the warehouse the “treatment room” and the “ebi”, a reference to a top security Dutch prison. The messages also revealed identities of potential victims, who were warned and went into hiding, police said.

Video released by the police showed heavily armed officers blasting open a door at the warehouse and discovering the improvised prison. Another armed team detained a suspect in Rotterdam.

“Six of the containers were intended as cells in which people could be tied up and one container was intended as a torture chamber,” Andy Kraag, the head of the police’s national investigation service, said in a video, adding that the police operation “prevented a number of violent crimes”.

A search of the containers uncovered bags containing tools including hedge cutters, scalpels and pliers. The items “were likely intended to torture victims or at least put them under pressure”, the police said.

In searches of other properties, including what police described as a base for the criminals near Rotterdam, officers found police uniforms and body armour, stolen vehicles, 25 firearms and drugs.

A court in Amsterdam ordered the six suspects to be held for 90 days as investigations continue.

“This is a great result of the 26Lemont investigation,” Kraag said. “And, take it from me, many more results will follow.”