John Pace, until recently UN human rights chief in Iraq, told the BBC News website that up to 75% of the corpses showed signs of extrajudicial death.

Mr Pace blamed an "endemic" breakdown of security for increasing violence.

"Anyone with a gun who is reasonably well organised can do whatever they want with impunity," he said.

Armed groups often threatened mortuary staff, aiming to stop autopsies and suppress evidence, Mr Pace said.

Iraq has seen a jump in apparently sectarian violence since the bombing last week of a Shia Muslim shrine in the city of Samarra.

But Mr Pace played down suggestions that Iraq was heading towards civil war, blaming a political vacuum and the collapse of law and order - rather than a generalised Shia-Sunni split - for the escalating violence.

'Chaotic'

Mr Pace described the Baghdad mortuary as a "barometer" of the situation in the city at any one time.

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http://news.bbc.co.uk/2/hi/middle_east/4765854.stm