Some of the human remains have identity cards attached

The desiccated remains were found in labelled plastic bags and unsealed hardboard coffins at the base near al-Zubayr in southern Iraq.

Several catalogues, with faded photographs presumably of the dead people, were also found.

Most of the corpses pictured appeared to have died from gunshot wounds to the head.

The area has been sealed off and is being treated as a mass war grave by UK troops, as experts try to determine how long they have been there.

The BBC's Ben Brown said local people had told him the remains were of Iraqi soldiers killed in the 1980-88 Iran-Iraq war, recently returned from Tehran.

And Qatar-based television channel al-Jazeera quoted an Iraqi official as saying the start of the US-led war had prevented the authorities from returning the bodies to their families.

Oliver Burch of UK-based charity Christian Aid said that theory was a possibility.

"About two months ago, after years of negotiations, an exchange of bodies had been arranged.

"The relationship between these countries has been so bad for so many years that such a thing as exchanging bodies hadn't been done on time."

Uprising speculation

But other reporters at the scene said some aspects of the base suggested a far more sinister history.

DISTURBING FIND 'These are all executions'

Hania Mufti of Human Rights Watch told the BBC it was possible the remains were of military or political enemies of Saddam Hussein.

"They were probably military personnel. It could be either persons who were accused or suspected of plotting against the Iraqi government or suspected of some other anti-government activity."

They could also have been victims of the failed Basra uprising against the Iraqi regime at the end of the first Gulf War in 1991, she said.

"From 1991 onwards there have been thousands of executions that have taken place after the uprising.

"It is possible that these may date back to 1991 when the uprising took place, or during the subsequent round-up of persons suspected of taking part - civilians or military personnel."

However, she said it was unusual to find the bodies of political prisoners killed by the regime unburied, and most would have been hanged rather than shot.

It could be persons who were accused or suspected of plotting against the Iraqi government, or suspected of some other anti-government activity Hania Mufti, Human Rights Watch

Reporters said they suspected at least some deaths had taken place on the premises.

Outside the warehouse was a wall dotted with a spray of bullet holes, most at head height, which one soldier said appeared to be a "purpose-built shooting gallery".

'Desecrated'

Tiny concrete cells were discovered nearby, some with pictures of Saddam Hussein and rusting metal hooks dangled from iron poles embedded in the ceiling.

One reporter said some of the faces in the photographs had been burned, mutilated or scarred with "horrific" injuries.

"Whoever they are, they have been desecrated in their death. No one should ever treat the dead like this," said Sergeant Simon Brain.

Although much of the complex was dilapidated, there was evidence that soldiers had lived in it until recently, with new army shirts found still in their bags.