More than 100 members of Australia’s mafia and bikie underworld have been arrested in the nation’s largest ever crime sting.

As part of a three-year collaboration between the Australian Federal Police (AFP) and Federal Bureau of Investigation (FBI), underworld figures were tricked into communicating via an encrypted app that had been designed by police.

The app, known as AN0M, was used by organised crime gangs around the world to plan executions, mass drug importations and money laundering.

Authorities were able to read up to 25 million messages in real time.

Police said they uncovered 21 murder plots and seized more than 3000 kilograms of drugs and $35 million in cash.

On Monday night, more than 300 search warrants were carried out across Australia, with simultaneous stings in the US and Europe.

Prime Minister Scott Morrison on Monday said the operation had “struck a heavy blow against organised crime. Not just in this country, but one that will echo around organised crime around the world”.

“This is a watershed moment in Australian law enforcement history,” Mr Morrison said.

“Our investments … have enabled [the AFP] to be part of major partnerships and take a leading role to spearhead this assault on organised crime.”

Minister for Home Affairs Karen Andrews said the statistics from the operation were “astounding”.

Triads, drug cartels exposed

The sting, known as Operation Ironside, has exposed criminals linked to South American drug cartels, Asian Triads and Middle Eastern and European criminal syndicates.

Dozens of members of the Comanchero and Lone Wolf outlaw motorcycle gangs were arrested.

The plan to use an encrypted app was hatched overseas over a few beers with FBI agents in 2018, before police figured out how to decrypt all messages.

The app was unwittingly distributed by fugitive Australian drug trafficker Hakan Ayik, after he was given the device by undercover agents.

Ayik, 42, recommended the app to criminal associates who would purchase the device pre-loaded with AN0M on the black market, allowing them to send messages, distort messages and take videos.

Police said in some cases it took months to establish whom a specific device was being used by.

About 4000 police raided properties this week, with the investigation growing so large the AFP paused its operations over the past few weeks, except for child protection and counter-terrorism.

More than 11,000 people were using AN0M devices across the world, including 1650 in Australia.

Half of the criminal activity detected on the app was in New South Wales.

Police conducted 210 search warrants on Monday, breaking the previous record of 50 search warrants in a single day.

Commissioner Kershaw said federal agents had been in the “back pockets” of criminals through the encryption app.

“The FBI had the lead on this. We provided the technical capability to decrypt those messages,” Commissioner Kershaw said.

“Some of the best ideas come over a couple of beers.”

The Commissioner said criminals on the app were “very brazen” with no attempt to hide activity through codified messages.

“All they talk about is drugs, violence, hits on each other, innocent people who are going to be murdered,” Commissioner Kershaw said.

“It was there to be seen.”

He said legal authorities prevented the app from being covertly used for a longer timeframe.

-ABC