A United Nations panel today made the strongest call yet on the United States to close down the Guantanamo Bay detention facility and to disclose the locations of all of its rumoured secret prisons abroad.

The committee said it was "deeply concerned" that detainees were being held at the prison camp in Cuba for protracted periods without proper legal safeguards or reliable judicial justification.

The ten members of the UN Committee Against Torture also called upon President Bush to end the use of torture and cruel treatment in interrogation of detainees, citing sexual humiliation, mock drownings and the use of dogs to induce fear.

In a 11-page report published today, the panel urged the US to reveal the location of any of the secret prisons, believed to be in Egypt, Jordan and Eastern Europe, to which suspects are allegedly transported by special rendition for interview under conditions which violate human rights conventions.

The panel has no legal power to enforce the US to abide by any of its demands, but it wields considerable moral authority.

For the first time in six years, the US sent a delegation of 30 officials to Geneva to defend its conduct at a hearing before the committee earlier this month. The delegation was criticised for refusing to comment on questions about secret prisons.

The report's findings will add to growing condemnation of America's activities in the War on Terror. It also stated that if proved, many of these actions could be in breach of international law.

The dossier said that there had been "reliable reports of acts of torture or cruel, inhuman and degrading treatment" by US military personnel in Iraq and Afghanistan. It said that some "have resulted in the death of some detainees during interrogation" and criticised vague US guidelines that "have led to serious abuse of detainees."

In a judgment which could also have implications for British efforts to deport foreign nationals suspected of terrorism-related offences, the report also demands detainees should not be returned to any state where they face a "real risk" of being tortured."

In its testimony, the US delegation told the committee that use of torture or inhumane and degrading treatment by the US military or intelligence services was outlawed, wherever they may be operating. The delegation also told the committee that 89 service personnel had been convicted in 103 courts martial as authorities attempted to root out abuse.

They included a series of prosecutions following revelations in 2004 of the mistreatment of Iraqi prisoners at Abu Ghraib prison, outside Baghdad, as well cases involving personnel in Afghanistan and Guantanamo Bay.

Nineteen of the convictions involved sentences of at least one year, while 28 personnel were thrown out of the US military, officials said. Nevertheless, the UN committee said it was "deeply concerned" at the "very lenient sentences" even after cases that had involved fatalities.

It added that such action did "not reflect the seriousness the state party claims in dealing with those abuses."

• Four Guantanamo prisoners tried unsuccessfully to commit suicide yesterday and several others attacked guards who rushed in to halt one of the bids, an attempted hanging, a camp spokesman said. The attempt took place in a medium-security area, where prisoners live in groups of up to 10 men in long bays lined with cot beds. Guards halted the attempted hanging, quelled the disturbance and moved the roommates to a maximum-security area.

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