Marine Corps Major Michael Mori was appointed by the Pentagon to represent David Hicks, a former Australian cowboy held at the US military prison camp in Cuba, as a "foreign combatant". He was captured in Afghanistan allegedly fighting for the Taliban.
Mori said the military tribunals for Guantanamo detainees were "definitely not fair" because they lacked the protection and independence of other courts. He also said because Hicks was a foreigner, he should be tried in his home country.
US servicemen detained by foreign countries could face similar treatment if captured, Mori warned.
"This commission process will set a bad example under which the unfair process or rules can be used to try US service members in the future by foreign countries," Mori told Australia's Nine Network television.
"Fighting for David Hicks to ensure he gets a fair process also benefits all US service members."
Hicks has been held for more than two years at the camp without being charged. He is among the first group of foreign detainees to receive legal representation and is expected to face a military commission soon.
Rights groups have protested against
conditions at Camp X-Ray, Cuba
Mori said Hicks did no harm to any US citizen or American soldier and should be tried in Australia, rather than the United States.
"If there's a valid international violation that the United States could try, it would be just as valid in Australia," Mori said.
The Australian government has said it does not have laws under which Hicks and fellow Australian detainee at Guantanamo Mamduh Habib, could be tried.
'Terror' links denied
It said recently it expected Habib also to receive legal representation and face trial, after officials from Canberra met with counterparts in Washington last month.
Habib's family denies he has any links with Usama bin Ladin's network, insisting when he was captured in Pakistan he was looking for a school for his children.
"This commission process will set a bad example under which the unfair process or rules can be used to try US service members in the future by foreign countries"
Hicks is among six Guantanamo Bay prisoners designated by US President George Bush as candidates for trials by the special military tribunals.
About 660 prisoners remain detained indefinitely. The US government has come under severe criticism by human rights groups for its treatment of the prisoners.