Human rights groups have asked the US to reveal the whereabouts of 39 people who have allegedly been held in secret CIA-run prisons.

A report compiled by six human rights groups listed the names of people who remain unaccounted for after having passed through US custody.

The groups urged the US to stop using secret prisons for terror suspects.

The US last year admitted the existence of such prisons in its "war on terror" but said they were no longer in use.

President George W Bush said last September that all secret prison sites were "empty".

The groups says they compiled their report, entitled Off the Record, from government and media sources and from interviews with former prisoners.

"It's time for the US government to come clean," said Clive Stafford Smith, Legal Director of Reprieve, one of the groups involved in the appeal.

"These 39 people have been missing for years, and the evidence shows they were in US custody at some point. Where are they and what has been done to them?"

Rendition flights

A spokesman for the CIA told the BBC News website that the CIA acts "in strict accordance with American law".

"Our counter-terror initiatives - which are subject to careful review and oversight - have been very effective in disrupting plots and saving lives," said CIA spokesman Paul Gimigliano.

The US administration has faced criticism from legal experts and human rights activists over its policy on detentions of terrorism suspects.

The human rights groups say that people have been arrested in countries including Pakistan, Iran, Iraq, Sudan and Somalia and flown in "extraordinary renditions" to secret US prisons.

A report approved by a European Parliament committee earlier this year said more than 1,000 covert CIA flights had crossed European airspace or stopped at European airports in the four years after the 9/11 attacks.

Last month, a US civil liberties group sued a subsidiary of Boeing for allegedly helping the CIA fly suspects to secret overseas detention centres where it says they were subjected to torture and abuse.

Three of the organisations - Amnesty International, the Center for Constitutional Rights and the International Human Rights Clinic of New York University School of Law - have filed a lawsuit under the US Freedom of Information Act for information on the missing people.

'Tough' interrogation

Human Rights Watch and Cageprisoners are the other two organisations seeking information on the 39 "ghost detainees".

The groups fears the missing people may have been moved to countries where they might be at risk of torture.

They say children as young as seven are among those detained.

"The duty of governments to protect people from acts of terrorism is not in question," said Claudio Cordone of Amnesty International.

"But seizing men, women and even children, and placing people in secret locations deprived of the most basic safeguards for any detainees most definitely is."

In September 2006, Mr Bush said 14 detainees had been held at secret CIA prisons that used interrogation methods that were "tough" but "lawful and necessary".

He said the prisoners had since been transferred to the US military prison at Guantanamo Bay, Cuba, and the CIA was not holding any more terror suspects.