In a report published on Monday the human rights group suggests that many detainees being held by the US-led multinational force (MNF) are trapped in a system of arbitrary detention with some being held without being charged for more than two years.
The report, entitled Beyond Abu Ghraib: Detention and torture in Iraq, also says there is mounting evidence of torture by Iraqi security forces, working alongside the MNF, including the so-called Wolf Brigade that reports to the Iraqi interior ministry.
The report lists allegations from former detainees who claim that they were beaten with plastic cables, given electric shocks and made to stand in a flooded room as an electrical current was passed through the water.
Amnesty also cited incidents when prisoners have died in custody and the deaths have yet to be fully investigated. The group said that investigations carried out by US and UK authorities into their own forces focused on junior military personnel.
Hassiba Hadj-Sahraoui, the deputy director of Amnesty's Middle East programme, said: "It is high time for all parties to the conflict to start observing the laws to which they have been and remain legally bound."
Amnesty said researchers conducted interviews in Jordan and Iraq with former detainees, relatives of current detainees and lawyers involved in detainees' cases in Iraq.
A US military detention mission spokesman responded to the report by saying that all detainees are treated according to international conventions and Iraqi law.
Lieutenant-Colonel Guy Rudisill said each detainee is given a form explaining the reasons for their imprisonment and their files are reviewed every 90 to 120 days.
The Amnesty report, quoting a US military website, said that figures compiled in November showed that the number of detainees in coalition military prisons in Iraq was 14,000. Last year, the US military said it planned to spend about US$50 million to expand prison capacity to hold up to 16,000 people.
Notorious photographs from 2003 showing Iraqi inmates being abused led to the convictions of several US soldiers and inquiries by US authorities into how prisoners are treated.
"It is high time for all parties to the conflict to start observing the laws to which they have been and remain legally bound"
The Amnesty report urges the British and US governments to declare publicly that torture and degrading treatment of prisoners will not be tolerated, to end indefinite internment of people in Iraq and to conduct impartial, transparent investigations of those accused of mistreating detainees.