In an open letter to US Defence Secretary Donald Rumsfeld, the New York-based rights watchdog on Thursday said hearings at the US Naval Base in Cuba in August had failed to meet basic standards for fair trials.
"The Guantanamo hearings clearly demonstrated that the military commissions lack competence, impartiality and fair rules of procedure," said Kenneth Roth, executive director of Human Rights Watch.
"It's time for the US government to put the military commissions out of commission."
Citing the observer it sent to monitor the hearings, Human Rights Watch said members of the commission had appeared visibly confused by questions about such basic legal issues as jurisdiction, and the applicability of the Geneva Conventions to armed conflict.
The watchdog also highlighted possibly prejudicial conflicts of interest arising from the fact that the four defendants currently before the commissions are all held in connection with the conflict in Afghanistan.
Some commission members are
said to have overlapping duties
"Several commission members had intelligence or combat responsibilities for this conflict, which raises questions about their ability to be impartial," it said.
Human Rights Watch raised further objections over US government translators, describing them as incapable of satisfactorily interpreting between Arabic and English.
"The Bush administration needs to reject these fundamentally flawed commissions," said Roth.
Sudanese al-Qusi was in the first
batch of hearings in August
"Justice can only be served if the US Government brings prosecutions that meet international fair trial standards. That means prosecution before federal criminal courts or courts-martial," he said.
The presidential decree that first set up the commissions was published in November 2001 in the aftermath of the 11 September 2001 attacks and the Afghanistan war.
Some 585 prisoners are being held in Guantanamo as suspected Taliban or al-Qaida fighters, most of them captured in the wake of a US-led invasion that drove the Taliban from power in Afghanistan.
The four detainees who figured in the first commission hearings last month were David Hicks, an Australian; two Yemenis, Salim Ahmad Hamdan and Ali Hamza Ahmad Sulayman al-Bahlul; and a Sudanese, Ibrahim Ahmad Mahmud al-Qusi.
"It's time for the US government to put the military commissions out of commission"
Executive Director, Human Rights Watch
Nearly all of the Guantanamo detainees have been kept for more than two and a half years without access to a lawyer or being informed of charges against them.
On Wednesday, a US federal court judge ordered the government to turn over or identify within 30 days all documents relating to the treatment of prisoners held at military bases and other detention facilities overseas, including Guantanamo Bay.
The documents had been requested under the Freedom of Information Act by the American Civil Liberties Union and other groups.
"If the documents are more of an embarrassment than a secret, the public should know of our government's treatment of individuals captured and held abroad," Judge Alvin Hellerstein said.
Some former Guantanamo detainees have levelled accusations of maltreatment and torture at the hands of their US interrogators - charges that have gained traction in the wake of the prisoner abuse scandal at the Abu Ghraib detention centre in Baghdad.