Federal police say the mammoth global sting they revealed on Tuesday prevented a plan for a mass shooting at an Australian cafe, as well as other murders and drug trafficking.

More than 200 members of Australia’s mafia and bikie underworld have been charged in the three-year covert operation, revealed by police on Tuesday.

As part of the collaboration between the Australian Federal Police and American Federal Bureau of Investigation, say underworld figures were tricked into communicating via an encrypted app that had been designed by police.

Police say murder plots, weapon purchases and drug trafficking were openly discussed on the encrypted platform, known as ANoM.

The surveillance has resulted in the arrest of more than 220 Australian organised crime figures since 2018 and is Australia’s largest undercover police operation.

More than 100 people have been charged.

Australian Federal Police deputy commissioner Nigel Ryan displays items seized during the raids. Photo: AAP

Offenders are linked to the Australian-based Italian mafia, outlaw motorcycle gangs, Asian crime syndicates and Albanian organised crime figures.

The communications found on the platform revealed 21 murder plots, gun distribution activity and mass drug trafficking, Australian Federal Police say.

The AFP also said on Tuesday it had seized 3.7 tonnes of drugs, more than 100 weapons and almost $45 million in cash as part of the operation since 2018.

The global operation has prompted mass arrests across 18 countries and the AFP intends to extradite and charge numerous residents overseas.

AFP Commissioner Reece Kershaw said organised crime figures openly and unashamedly discussed their activities on the ANoM platform, unaware police were monitoring their discussions.

After precursor encryption platform Phantom Secure was shut down by authorities in 2018, the Federal Bureau of Investigation commandeered and secretly managed ANoM, allowing it to organically grow in the criminal underworld.

The app – which required installation on mobile phones stripped of other capabilities – became increasingly popular among organised crime figures as it was spruiked by their colleagues, according to Mr Kershaw.

This snared the crime figures on ANoM in an ever-expanding net as the AFP took the lead on decrypting and reading their communications in real-time.

“We allege they’ve been trafficking illicit drugs into Australia at an industrial scale … criminal gangs are targeting Australia because it is one of the most profitable countries in the world to sell drugs,” Mr Kershaw said.

“Australian law enforcement has been arresting and charging alleged offenders and we have prevented tonnes of drugs from coming onshore.

“We’ve arrested the alleged kingmakers behind these crimes, prevented mass shootings in suburbs, frustrated organised crime by seizing ill-gotten wealth.

“We have been in the back pockets of organised crime.”

Police say they seized $45 million in cash during the three-year operation. Photo: AAP

Mr Kershaw said the mass shooting disrupted by police included organised crime activity with a machine gun at a suburban cafe.

He also revealed an unnamed outlaw motorcycle gang in Australia was making $20 million a month from drug peddling.

Mr Kershaw said more ANoM-related arrests were looming, but warned the platform was relatively small compared to others used by the underworld, which remain out of the reach of law enforcement.

ANoM made up 5 per cent of encrypted communications domestically.

He also warned of intelligence implying some “trusted insider threat”, with the Australian Commission for Law Enforcement Integrity investigating.

Prime Minister Scott Morrison said the Australian law enforcement operation, known as Operation Ironside, struck a “heavy blow” against gangs.

He said his government had a zero-tolerance approach to gang activity and police had taken “great risks” to see the investigation through.

“The operation puts Australia at the forefront of the fight against criminals who peddle in human misery and ultimately, it will keep our communities and Australians safe,” Mr Morrison told reporters on Tuesday.

“Illicit drug use ruins lives and fuels organised crime.”

New Zealand authorities have also arrested 35 people for alleged drug dealing and money laundering, seizing some $NZ3.7 million ($A3.4 million) in assets.

European Union police agency Europol and the FBI will hold their own press conferences on the matter on Tuesday and Wednesday (Australian time).

-with agencies