The UN's human rights official in Iraq has said the Iraqi authorities are illegally holding thousands of people.
The UN says 29,565 people are detained by Iraqis and coalition forces
Gianni Magazzeni said that of the 15,000 people held under Iraqi control, little more than half were under the jurisdiction of the justice ministry.
This is the only body with the right to detain suspects for more than 72 hours.
But he said thousands were also being detained by the interior ministry and hundreds by the defence ministry, in clear breach of Iraqi law.
29,565 people detained in Iraq
8,300 held legally by the Iraqi justice ministry
14,222 held by coalition forces
6,000 held by Iraqi interior ministry
460 are held by Iraqi defence ministry
More than 14,000 people are also being held by US-led coalition forces in Iraq.
Mr Magazzeni said the UN believed that number was far too high and he urged the US military authorities to either charge or release them.
"We think that the 15,000 being held for 'urgent security reasons' are far too many and we are working very closely [with the coalition] to reduce that number considerably," Mr Magazzeni said.
'Torture and execution'
He said the UN still did not have access to prisoners being held in unidentified coalition prisons, and called for them to be released or handed over to Iraqi authorities to be charged.
"We want them to speed up this process," Mr Magazzeni said. He added that the UN was "very concerned about ongoing violations" of human rights in Iraq.
"Torture and summary executions happen every day," Mr Magazzeni said.
There have been widespread and recurring reports of death squads, allegedly linked to Shia political factions, targeting Sunni Iraqis.
Mr Magazzeni said the so-called death squads had become more active in Iraq since the bombing of the revered Shia shrine at Samarra in February.
"We've seen an increase in the instances of allegations of actions by such militias or death squads that sometimes are linked with police forces or forces within state entities in Iraq," he said.