In Iraq, "one of the major human rights challenges remains the detention of thousands of persons without due process," Secretary-General Kofi Annan said in a report to the 15-nation U.N. Security Council.

According to the Iraqi Justice Ministry, there were about 10,000 detainees in all of Iraq as of April, "6,000 of whom were in the custody of the Multinational Force" commanded by the United States, Annan said.

"Despite the release of some detainees, their number continues to grow. Prolonged detention without access to lawyers and courts is prohibited under international law including during states of emergency," his report said.

A Security Council resolution adopted a year ago ending the U.S.-led occupation of Iraq let the U.S. military keep taking and holding prisoners even after the June 2004 handover of power to Iraqis, in apparent contradiction of the Geneva conventions.

The United States at the time of the handover held more than 8,000 "security and criminal detainees" in U.S.-controlled centers including the now-infamous Abu Ghraib detention center, where photographs of prisoners taken by U.S. soldiers documented a variety of gruesome human rights abuses.

Amnesty International last month cited Abu Ghraib and a second U.S. detention center in Guantanamo Bay, Cuba, as evidence that Washington "thumbs its nose at the rule of law and human rights," a charge dismissed as "absurd" by President Bush.

While the 2004 U.N. resolution was silent on the issue of U.S. military prisons, a side letter from then-Secretary of State Colin Powell authorized the U.S.-led forces in Iraq to undertake a variety of tasks linked to "the maintenance of security" including "internment where this is necessary for imperative reasons of security."

The Fourth Geneva Convention, while allowing occupying forces to detain individuals, has no provision for internment by outside forces after an occupation has ended.