The UN Committee on Civil and Political Rights, which monitors compliance with a 1976 treaty guaranteeing basic freedoms, said Washington was already six years late in filing a regular report on its adherence.

"If a full report can't be done by the end of the year at least they should address ... problems of legal status and treatment of persons detained in Afghanistan, Guantanamo Bay, Iraq and other places of detention outside the United States," Sir Nigel Rodley, a British expert on the committee, told a news briefing.

US forces are holding hundreds of terror suspects in Afghanistan, the US naval base in Guantanamo, Cuba and Iraq, most without charge or legal representation, activists say.

Photographs of US soldiers abusing Iraqi detainees at Abu Ghraib prison near Baghdad sparked world outrage in May. Pentagon investigations have led to three convictions so far.

The committee, which has no powers of sanction, received the last US report in 1994. Reports are generally due every four years on the right to life, self-determination and due process, and freedom of movement, expression and religion in a country.

Rodley, who told journalists the committee had written to the United States, said it was also seeking information on the US Patriot Act, a cornerstone of the US war on terror.

Critics including the American Civil Liberties Union say that it gives the FBI unchecked powers of surveillance at home.

A spokeswoman at the US diplomatic mission in Geneva said that Washington intended to file its report in the next few months. "This follow-up response will address questions on all relevant activities of the US armed forces," Brooks Robinson told Reuters.

The committee has also scrutinized records from five of the 153 states to have ratified the International Covenant on Civil and Political Rights: Albania, Benin, Finland, Morocco and Poland.

It expressed concern at Morocco's counter-terrorism legislation adopted following an attack in Casablanca in May 2003 that killed 45 people. The law allows suspects to be held up to 12 days in preventive detention without access to a judge.

Some 2,000 suspected Islamist militants have been arrested since then, and many have been subjected to threats and abuse, according to the New York-based group Human Rights Watch.

"We are concerned about the extensive period of preventive detention ... which is frankly a license to torture, or is often perceived that way by law enforcement officials," said Rodley, who served eight years as UN special investigator on torture.

The committee also said it was concerned about "numerous allegations of torture" of detainees in Morocco and at bans on marriage between a Muslim woman and a non-Muslim, and on a Muslim changing religion.

"This of course raises concerns about the total respect of freedom of religion," said committee expert Rafael Rivas Posada.