The National Crime Agency and police during raid on a property in Birmingham, UK.
London CNN  — 

An encrypted messaging service used exclusively by criminals has been infiltrated by police in a major operation, leading to hundreds of arrests and the seizure of firearms, drugs and millions of dollars in cash.

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 NCA said it had made 746 arrests, and seized £54 million ($68 million) in cash, 77 firearms and more than two tons of drugs during the unprecedented Operation Venetic.

Police seized sub-machine guns, handguns, four grenades, an AK47 assault rifle and more than 1,800 rounds of ammunition during the operation, as well as more than 28 million Etizolam pills (street valium) from an illicit laboratory.

They also seized 55 high-value cars, and 73 luxury watches, the NCA said.

The crime agency said it had worked with police partners to prevent kidnappings and executions by “successfully mitigating over 200 threats to life.”

UK Home Secretary Priti Patel tweeted that she had joined police in a dawn raid Thursday and congratulated the agency on its work.

“This operation demonstrates that criminals will not get away with using encrypted devices to plot vile crimes under the radar,” she said in a statement.

Police in the Netherlands said they had made 60 arrests during their investigation, codenamed “Lemont,” and had seized 25 tons of drugs, 20 million euros ($23 million), dozens of automatic weapons, 25 cars and expensive watches.

In a joint news conference with European law enforcement agencies, Dutch police said 19 synthetic drugs labs had been dismantled and more arrests were expected.

EncroChat infiltrated

Operation Venetic – the biggest-ever operation of its kind in the UK – began in 2016, the NCA said, with international law enforcement agencies targeting EncroChat and sharing intelligence.

Two months ago, agencies in France and the Netherlands infiltrated the platform and shared the data via Europol, allowing police to monitor the private communications – including photos and millions of messages – of criminals.

The operators of EncroChat, which is run from outside the UK, realized the platform had been penetrated on June 13 and sent a message to its users urging them to throw away their handsets, according to the NCA.

The Met Police said it had arrested some of the capital’s “longest-standing and most dangerous criminals,” who are linked to violent crime and importing Class A drugs, and “lead lavish lifestyles and live in multi-million pound properties.”

It said there would be more arrests and seizures in the coming weeks and months.

The force’s police commissioner Cressida Dick said in a statement: “This operation is the most significant activity, certainly in my career, we have ever carried out against serious and organized criminality across London.

“Organized crime groups have used encrypted communications to enable their offending. They have openly discussed plots to murder, launder money, deal drugs and sell firearms capable of causing atrocious scenes in our communities. They were brazen and thought they were beyond the reach of the law,” she added.

The EncroChat servers have now been shut down. The handsets used cost around £1,500 ($1,870) for a six-month contract and came with pre-loaded apps for instant messaging, the ability to make calls and a kill code so they could be remotely wiped.

Recent messages from some of the UK handsets included, “This year the police are winning,” and, “The police are having a field day,” according to the NCA.

‘Victory against the kingpin criminals’

The UK’s National Police Chiefs’ Council lead for serious organized crime, Chief Constable Steve Jupp, said the “unique operation” was focused on those believed to be at the highest level of organized crime.

He said the work was “the culmination of meticulous planning” and represented an “unparalleled victory against the kingpin criminals whose criminal activity and violence intimidates and exploits the most vulnerable.”

“By dismantling these groups, we have saved countless lives and protected communities across the UK,” he added.

NCA Director of Investigations Nikki Holland said the infiltration of the “command and control” communication platform was “like having an inside person” in every top organized crime gang. Holland said criminals with encrypted devices “should be very, very worried.”

CNN’s Niamh Kennedy contributed reporting.