The so-called "Guantanamo protocols" -- sleep and sensory deprivation, prolonged isolation and death threats -- have been applied to mainland prisons despite attempts by some military personnel to improve harsh conditions, the American Civil Liberties Union (ACLU) and the Allard K. Lowenstein International Human Rights Law Clinic at Yale Law School said in a statement.

The military documents, including regular emails between military officers, were obtained under the Freedom of Information Act, and detail the detention and interrogation at naval prisons in Virginia and South Carolina.

They focus on three "enemy combatants:" two US citizens, Jose Padilla and Yaser Hamdi, and a legal resident, Ali al-Marri.

"Guantanamo was designed as a law-free zone, a place where the government could do whatever it wanted without having to worry about whether it was legal," said Jonathan Freiman, an attorney with the Lowenstein Clinic.

"It didn't take long for that sort of lawlessness to be brought home to our own country."

"Who knows how much further America would have gone if the Supreme Court hadn't stepped in to stop incommunicado detentions in 2004," added Freiman.

According to the documents, some US military officers expressed doubts about applying Guantanamo-style rules in mainland prisons, the rights groups said.

Officers particularly expressed "grave concern" that the solitary confinement imposed on US soil was more extreme than in Guantanamo, the civil rights groups said.

"Navy officers also exhibited frustration with the Defense Department's unwillingness to provide the detainees with access to legal counsel or any information about their fates," it said.

Guantanamo prison was established in the aftermath of the September 11, 2001 attacks.

"The application of Guantanamo protocols on US soil is incredibly significant and indicates how far the administration has gone in terms of suspending the law," said Jonathan Hafetz, an attorney with the ACLU's National Security Project.

"The Bush administration has long argued that detainees held in Guantanamo are not entitled to any constitutional protections ... an argument the Supreme Court has recently rejected," he added.

"But this is not even Guantanamo. We are talking about creating prisons beyond the law right here in America."

The ACLU noted that the documents detail conflict throughout the military's chain of command on applying the procedures on US soil.

"Though Navy personnel tried several times to improve the harsh conditions under which Hamdi, Padilla and al-Marri were detained, senior Defense Department officials repeatedly denied the requests," said the ACLU.

While in the US prisons, Padilla and al-Marri reported being subjected to the interrogation techniques used at Guantánamo Bay including "sleep deprivation, painful stress positions, prolonged isolation, extreme sensory deprivation, and threats of violence and death," it said.

The trio were picked up in the wake of September 11 for associations with Al-Qaeda.

Hamdi has since been handed over to Saudi Arabia, and Al-Marri and Jose Padilla remain in prisons on the US mainland.