Australian law enforcement agencies are increasingly unable to monitor the communications of some of the country's most powerful criminals due to the rising prevalence of uncrackable encrypted phones.

The phones are linked to a series of the underworld killings that rocked Sydney, several senior law enforcement officials told the ABC on condition of anonymity.

The phones are sold by dozens of companies worldwide and have legitimate uses.

But the law enforcement officials say thousands of the phones have been obtained by Australian criminals and they are using them to commit serious crimes, including murder.

One company is Phantom Secure, a Canadian-based seller of encrypted Blackberries.

The ABC does not suggest the company itself is aware its products are being used by criminals, only that criminals have become aware of the phone's utility and have taken advantage.

Phantom Secure did not respond to requests for an interview or to questions sent by the ABC.

The Phantom Blackberries cost up to $2,760, which includes a six-month subscription to the company's data service.

At the end of that subscription a user can spend a further $2,000 to renew their six-month subscription.

The Phantom phones have the microphone and camera removed and cannot be used to surf the web, send emails or texts or make calls. The only thing they can do is send messages using a private messaging system.

That system is protected by military-grade encryption and cannot be hacked even by Australia's electronic spy agency, the Australian Signals Directorate, said a Government official who declined to be named.

"Our intelligence would suggest that the most serious of crimes are being facilitated by... encrypted communications," Paul Jevtovic, the acting head of the Australian Crime Commission (ACC), said.

"We're talking about acts of violence; we're talking about a range of serious crime."

Phantom phone use suspected in hits on Hells Angels bikies

In particular, the ABC has learned that a well-known member of the Comanchero Motorcycle Club is suspected of ordering at least two high-profile killings in recent years using his encrypted Phantom Secure phone.

Those murders were of Tryone Slemnik, a newly minted Hells Angel member gunned down during a drive-by in Sydney's south in July last year, and Roy Yaghi, a Hells Angels associate and convicted drug cook who was shot dead in 2012 while sitting in a ute in Sydney's west.

NSW police are aware of a connection between the well-known Comancheros and the two killings, but have been stymied in their investigations due to the suspected use of the Phantom phone.

The ACC has launched several investigations into the use of encrypted communications and told the ABC the issue is a growing problem.

"Organised crime [has] seen that encrypted communications can allow them to plan and execute their criminal activities and prevents law enforcement detection. So clearly that's of concern to us; it has been for some time," Mr Jevtovic said.

"It's estimated that that in the next two years the [global encryption] market will double in size, which means there's a strong demand out there.

"Now whilst that demand is from legitimate industry and citizens who are not involved in crime, our concern is that organised crime will further avail themselves of this technology."

Two federal parliamentary committees recently recommended the Government undertake wholesale reform to the legislation that regulates how police and intelligence agencies can monitor people's phones, the 1978 Telecommunications (Interceptions and Access) Act, in the hope of clawing back some ground from criminals using the high-tech phones.

"The rapid uptake of new communication technologies and encryption by organised crime and terrorist groups is a significant concern and the Attorney-General's Department is currently pursuing reforms to the telecommunications interception legal framework," Justice Minister Michael Keenan said.

ASIO and the federal police declined to comment about the issue. The Australian Signals Directorate told the ABC they were aware of Phantom Secure but also turned down an interview.