A London-based human rights group accused the US military of failing to adequately investigate the latest allegations of prisoner abuse at Guantanamo Bay and urged officials to open the detention centre to more independent monitors.

An Army officer’s investigation into allegations that guards bragged about beating Guantanamo Bay detainees has found no evidence of mistreatment, military officials said today.

The US Pentagon has ordered an investigation into possible abuse at the Guantanamo Bay prison after a Marine officer said she overheard guards boasting about beating detainees.