The torture of prisoners in US custody in Iraq was authorised and routine even after the Abu Ghraib scandal came to light, a US-based rights group says.
Abuses at Abu Ghraib were blamed on a few rogue US soldiers
Soldiers' accounts show that detainees routinely faced severe beatings, sleep deprivation and other abuses for much of 2003-2005, Human Rights Watch says.
Soldiers who tried to complain about the abuse were rebuffed or ignored.
But a Pentagon spokesman said 12 reviews had found there was no policy condoning or encouraging abuse.
"The standard of treatment is and always has been humane treatment of detainees in [Department of Defence] custody," Lt Col Mark Ballesteros told Reuters news agency.
John Sifton, author of the Human Rights Watch (HRW) report, said the accounts given to the group by former US soldiers revealed the opposite.
"These accounts rebut US government claims that torture and abuse in Iraq was unauthorised and exceptional - on the contrary, it was condoned and commonly used," he said.
Photos showing US soldiers abusing and sexually humiliating Iraqi prisoners at the Abu Ghraib prison near Baghdad in 2004 shocked the world.
Eleven US soldiers have now been convicted in connection with the abuse. No senior officers have so far been convicted.
The HRW report gives first-hand accounts of abuses at a detention centre at Baghdad airport called Camp Nama, as well as a facility near Mosul airport and a base near al-Qaim on the Syrian border.
An interrogator posted at Mosul in 2004 told HRW that he and his fellow interrogators had been told by the officer in charge of their unit to use abuse techniques on some detainees.
ABU GHRAIB CONVICTIONS
May 04: Spc Jeremy Sivits - 1 year jail, bad conduct discharge
Sept 04: Spc Armin Cruz - 8 months jail, bad conduct discharge
Oct 04: Sgt Ivan Frederick - 8 years jail, dishonourable discharge
Oct 04: Spc Megan Ambuhl - fine, other than honourable discharge
Jan 05: Spc Charles Graner - 10 years jail, dishonourable discharge
Feb 05: Spc Roman Krol - 10 months jail, bad conduct discharge
Feb 05: Sgt Javal Davis - 6 months jail, bad conduct discharge
Sept 05: Pte Lynndie England - 3 years jail, dishonourable discharge
May 05: Spc Sabrina Harman - 180 days jail, bad conduct discharge
Mar 06: Sgt Michael Smith - 179 days jail, bad conduct discharge
Jun 06: Sgt Santos Cardona - 90 days labour, $7,200 fine
He described how they used dogs to intimidate the detainees, had them walking on their knees in the gravel and standing for extended periods with arms outstretched holding water bottles.
An interrogator at Camp Nama said the use of abuse techniques was commonplace - authorisation forms could be easily prepared for commanding officers to sign.
"I never saw a sheet that wasn't signed," the soldier said.
HRW gives accounts of instances where soldiers who were concerned by the abuses were thwarted from reporting it.
One military police guard at the facility near Qaim, who took his concerns to an officer, was reportedly told: "You need to go ahead and drop this, sergeant."
HRW says its findings show that criminal investigations of abuses need to follow the military chain of command, rather than focusing on lower-ranked soldiers.
The New York-based organisation calls on the US Congress to appoint an independent commission to investigate the extent of the problem, and urges US President George W Bush to appoint an independent prosecutor to investigate and prosecute perpetrators of the abuse.
"It is now clear that leaders were responsible for abuses in Iraq," Mr Sifton said. "It's time for them to be held accountable".
The Bush administration has faced intense and sustained international criticism for its treatment of prisoners - in Iraq, Afghanistan and at Guantanamo Bay in Cuba.
Earlier this month, the White House announced that all US military detainees would be treated in line with the minimum standards of the Geneva Conventions.
The shift in policy came almost two weeks after the US Supreme Court ruled that the conventions applied to detainees.
The Geneva Conventions, which were passed in the wake of World War II, are meant to guarantee minimum standards of protection for non-combatants and former combatants in war.