A complaint has been filed to the United Nations on behalf of former US Marine Daniel Duggan, who is incarcerated in a notorious wing of NSW’s Silverwater Prison while he awaits an extradition attempt.

The 54-year-old was arrested by Australian authorities last year under an agreement with the US government, which has accused him of training pilots for the Chinese military.

After his arrest, Mr Duggan was classified an “extreme high risk” and placed in segregation in a two-by-four-metre cell in Silverwater’s Metropolitan Remand and Reception Centre, according to his supporters.

Despite his inmate classification since being downgraded, his lawyers have argued his ongoing custodial conditions constitute a violation of the International Covenant on Civil and Political Rights (ICCPR).

Mr Duggan’s wife Saffrine said after four months being held in maximum security alongside “terrorists, murderers, pedophiles”, her husband was a shadow of his former self.

“I was shocked when I saw Dan recently. He’s trying to fight this injustice but he’s a shadow of himself,” she said.

“This is unprecedented and an affront to Australia’s rule of law and manipulation of the Australian legal system by the US, at the expense of the Australian taxpayer.”

AAP has approached Corrective Services NSW for comment.

Those fighting for Mr Duggan’s release say his conditions constitute several violations of the ICPPR, by failing to protect him from inhumane or degrading treatment and not segregating him from convicted prisoners.

The complaint also claims the conditions violate his right to adequate facilities for the preparation of his defence and to confidential communication.

Mr Duggan, who became an Australian citizen in 2012, claims the US charges are politically motivated.

Mrs Duggan said she had only been able to see her husband twice since his incarceration and their six children were becoming increasingly distressed by their father’s absence.

The matter of Mr Duggan’s eligibility for extradition will next come before a magistrate at Downing Centre Local Court on March 20, but the decision will ultimately be made by Attorney-General Mark Dreyfus.

-AAP