· Try detainees or release them, says report · Prisoners' treatment 'amounts to torture' · Bush government dismisses report

The United States should close down its detention camp in Guantánamo Bay and give its detainees an independent trial or release them, a United Nations report released today suggests.

The 54-page report called on Washington "to close down the Guantánamo Bay detention centre and to refrain from any practice amounting to torture or cruel, inhuman or degrading treatment".

The UN commission on human rights report was based on interviews with former detainees, public documents, media reports, lawyers and a questionnaire filled out by the US government.

The five envoys from the commission said photo evidence alone - corroborated by testimony of former prisoners - had shown detainees were shackled, chained, hooded and forced to wear headphones and goggles.

"Such treatment amounts to torture, as it inflicts severe pain or suffering on the victims for the purpose of intimidation and/or punishment," the report said.

Some of the interrogation techniques used at the detention facility itself - particularly the use of dogs, exposure to extreme temperatures, sleep deprivation for several consecutive days and prolonged isolation - caused extreme suffering.

The simultaneous use of such methods was "even more likely to amount to torture," it said.

This afternoon, the Bush administration rejected the recommendation to shut the prison.

"These are dangerous terrorists that we're talking about that are there," said White House spokesman Scott McClellan.

He dismissed the report as "a rehash" of allegations that have been made previously by lawyers for some Guantánamo detainees, saying the military treats all detainees humanely.

"We know that al-Qaida terrorists are trained in trying to disseminate false allegations," Mr McClellan said.

The US ambassador to the UN in Geneva, Kevin Moley, said the investigation had taken little account of evidence provided by the US.

He also said the five envoys on whose investigations the report was based on had rejected an invitation to visit the detention centre in the US's Cuban enclave. The envoys said they had turned it down because the US would not permit them to interview detainees.

Only the International Committee of the Red Cross has been allowed to speak to detainees, but the organisation keeps its findings confidential, reporting them solely to the detaining power. Some reports have been leaked by what the organisation calls "third parties".

Clive Stafford-Smith, the legal director of Reprieve and who represents 40 detainees, welcomed the report.

"This is another authoritative body speaking and it's absolutely right, they should shut the place down. The question now is whether the Bush administration are going to listen or do what we have always seen and bluster against the UN."

Mr Stafford-Smith said he had witnessed the force-feeding highlighted in the report when he went to see a client.

"He had a tube up his nose which he pulled out in an excruciating way. He told me they had beat him up to force-feed him."

Stephen Bowen, Amnesty International UK's campaigns director, said Guantánamo was "unreformable".

"After four years Guantánamo has become a byword for abuse and an indictment of the US government's failure to uphold human rights in the 'war on terror'. The US authorities should immediately close down the camp and either release prisoners or bring them before proper courts on the US mainland.

Manfred Nowak, who co-wrote today's report, said the US must now accept that international human rights law was applicable to Guantánamo Bay.

"Those persons are arbitrarily detained and therefore have to be released or brought to an independent court for being charged and convicted," he said, adding that combined interrogation techniques, explicitly authorised by the US defence secretary, amounted to degrading or inhuman treatment. He said in some cases it amounted to torture.

He told BBC Radio 4's the World at One he had "a lot of objective evidence" to back up his claims and said if the US had nothing to hide it should allow his colleagues full access to the camp.

The report also disputes the Bush administration's legal arguments for the prison, sited at a navy base in Cuba with the purpose of remaining outside the jurisdiction of US courts.

During an 18-month investigation, the envoys interviewed freed prisoners, lawyers and doctors to collect information on the detainees, who have been held for the last four years without access to US judicial oversight.

The report lists techniques in use at Guantánamo that are banned under the UN's convention against torture, including prolonged periods of isolation, exposure to extremes of heat and cold, and humiliation, including forced shaving.

It also focuses on a relatively new area of concern - the resort to violent force-feeding to end a hunger strike by inmates. Guards began force-feeding protesters last August, strapping them on stretchers and inserting large tubes into their nasal passages, according to a lawyer for Kuwaiti detainees who has had contact with the UN envoys.

The report adds to a body of evidence about mistreatment. The report by the International Committee of the Red Cross last year said interrogation techniques there were "tantamount to torture".