The lawyer for a former US military pilot arrested in Australia and facing possible extradition to the US said his client was wrongly classified as an "extreme high risk" prisoner, and he had asked the attorney-general to release him.

Former US Marines pilot Daniel Edmund Duggan was arrested in New South Wales in October at the request of the US government, the same week Britain announced a crackdown on its former military pilots working to train Chinese military fliers.

The US States must lodge an extradition request for Duggan by December 20 under a bilateral treaty, a Sydney court was told on Monday. The case was adjourned until December 16.

Duggan's lawyer Dennis Miralis, said he was classified by the prison system as "extreme high risk" and was denied access to pens and stationery and had been refused medical treatment.

"This is unprecedented to have an Australian citizen placed on the most strict inmate restrictions, akin with people who have been convicted of terrorist offences and multiple homicides, in circumstances where he has never been in trouble with police," Miralis told reporters outside court.

Duggan, who denies breaching any law, is an Australian citizen and had renounced his US citizenship, he said. Details of the arrest warrant and the charges he faces in the US are sealed.

Reuters previously reported Duggan moved from Australia to China in 2014 to work as an aviation consultant, and shared a Beijing address with Chinese businessman Su Bin, who was jailed in the US in 2016 in a high-profile hacking case involving the theft of US military aircraft designs.

Duggan and Su Bin had also worked a decade ago for a South African flight school that is under scrutiny by British authorities for training Chinese military pilots, Reuters reported.

Miralis said on Monday he had no details why the US was seeking the extradition of his client.

"Trying to speculate how the case against Mr Duggan might ultimately be construed or framed is unprofitable because we don't have the facts," he told reporters.

He had written to the attorney-general seeking Duggan's release, and lodged a complaint with the inspector general of the intelligence services over "the way in which Australian national security agencies have behaved in relation to Mr Duggan", he told the court.

The Australian government's lawyer Trent Glover told the court this was "an ordinary, usual extradition process where we are awaiting receipt of an extradition request".

Duggan's classification while in custody had no connection to his extradition, he said.

Corrective services New South Wales, which runs prisons, said it didn't comment publicly on inmate classifications.

The attorney-general's spokesperson told Reuters it was "not appropriate to comment on Mr Duggan's extradition proceedings, given this matter is currently before the courts".

Reuters