(CNN) Authorities in the Netherlands have discovered an apparent torture site hidden inside shipping containers, which were lined with sound-proofing material and filled with assumed torture devices, the country's National Prosecutor's Office has said.
Officers raided the site at Wouwse Plantage on the Dutch-Belgian border on June 22, arresting six men suspected of kidnapping and hostage taking.
They found six shipping containers which had been converted to what are believed to be "prison cells," as well as a stash of weaponry including pruning shears and loppers.
"In each of the cells, handcuffs were attached to the ceiling and floor, in order to be able to chain someone standing up with their arms raised," the statement said. "The rooms were finished with noise isolating panels and heat-insulating foil."
One of the units also contained a dental chair, with straps for feet and arms. "The sea container with the dental chair contained bags with objects that were presumably intended to torture or at least put pressure on victims," the statement added.
"The police found, among other things, pruning shears, loppers, a branch saw, scalpels, pliers, extra handcuffs, fingercuffs, tape, balaclavas, and black cotton bags that can be pulled over the head. During a search at a home in Rotterdam, 24 kilos of MDMA was also found."
The containers were also fitted with cameras for remote monitoring.
Officers also found three stolen delivery vans, two BMWs, seven handguns and a Chinese variant of the AK-47. "In total, 25 weapons were found with the suspects," the National Prosecutor's Office said.
Authorities say the investigation began in April, during which officers were able to access an encrypted chat network -- EncroChat -- to track the group's movements and plans. "From this it could be deduced who the intended victims were," the statement said.
"They were warned by the police and went into hiding elsewhere. As a result, and thanks to permanent CCTV surveillance in and near the warehouse, planned kidnappings, hostage-taking and other serious violent crimes were prevented."
EncroChat, which offered a secure mobile phone instant messaging service, was a "criminal marketplace" used by 60,000 people worldwide for coordinating the distribution of illicit goods, money laundering and plotting to kill rivals, according to the UK's National Crime Agency (NCA).
The discovery of the containers followed a series of successful raids by UK and European police based on information from the network, which saw hundreds arrested and more than 27 tons of drugs seized in the UK and Netherlands.
The six men who were arrested in relation to the apparent torture site are all from The Netherlands. An Amsterdam court on Monday ordered their detention for 90 days.