Attorney-General George Brandis has joined calls for Apple to comply with an FBI request to unlock an iPhone used by one of the shooters in December's San Bernadino massacre.

Key points: Apple rejects court order to help FBI investigate shooter's phone

Apple rejects court order to help FBI investigate shooter's phone CEO says request 'threatens the security' of Apple customers

CEO says request 'threatens the security' of Apple customers FBI investigating possible communication between shooters and Islamic State

FBI investigating possible communication between shooters and Islamic State In a previous case, Apple said it was 'impossible' to unlock devices using their new operating system

Apple's chief executive Tim Cook released a statement announcing the company would contest a court order to help the FBI break into a phone recovered from Syed Rizwan Farook, one of the San Bernardino shooters.

The company was ordered to provide "reasonable technical assistance" to investigators seeking to unlock the data on Farook's iPhone 5C.

Mr Cook argues the FBI's demand threatens the security of Apple's customers but he has already been criticised by a presidential candidate and New York's police chief for the taking the stance.

The company's refusal to cooperate with the FBI has been criticised by a cast of characters including New York Police Commissioner Bill Bratton and presidential candidate Donald Trump who suggests unlocking the iPhone is "common sense".

"We have to be very careful, we have to be very vigilant, but to think that Apple won't allow us to get into her cell phone — who do they think they are? Now we have to open it up," Mr Trump said.

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New York Police Commissioner Bill Bratton says the issue needs to be resolved.

"We are increasingly blind for terrorism purposes and for general law enforcement purposes with the new devices and the continuing effort to make them even more secure against even court orders authorising law enforcement to have access," Mr Bratton said.

'All orders of courts should be obeyed by any party': Brandis

Now Senator Brandis has joined the calls for Apple to comply, saying all companies in the tech sector should cooperate with investigations into serious crime.

"We would expect, as in Australia, that all orders of courts should be obeyed by any party which is the subject of a lawful order by a court," he told ABC correspondent Michael Vincent.

Senator Brandis said while particular facts of this case were not relevant to Australia, the situation illustrated we were in a time "when encryption of data is becoming almost ubiquitous and vast quantities of data which would previously have been accessible by warrant to law enforcement agencies inaccessible".

"I think it shows how important it is that ISPs do cooperate with law enforcement agencies in facilitating and cooperating with proper investigations into serious crime," he said.

The FBI is investigating Syed Farook and his wife, Tashfeen Malik, over potential communications with Islamic State ( ABC America/DMV, file photo )

Although Senator Brandis said he is not proposing similar compliance in Australia, adding a problem like this has not yet arisen in Australia.

"My department has established very cooperative and collaborative relationships with companies in the tech sector and we're happy with the level of cooperation we are receiving," Senator Brandis said.

"But nevertheless, there is a broader problem for law enforcement in all jurisdictions.

"Frankly, if data is encrypted in a way that is entirely inaccessible, without the cooperation of the ISP or the maker of the device, then that makes inaccessible relevant investigative information that would hitherto have been accessible and that's a problem for law enforcement."

Federal prosecutors in Los Angeles requested the court order to compel Apple to assist the investigation into the December 2 shooting rampage by Farook and his wife that killed 14 people and injured 22 others.

The two were killed in a shootout with police.

The FBI has been investigating the couple's potential communications with the Islamic State and other militant groups and treating the case as an incident of domestic terrorism.

"Apple has the exclusive technical means which would assist the government in completing its search, but has declined to provide that assistance voluntarily," prosecutors said.