The US government has admitted that a top spy agency was using a “crucial tool” against terrorism by sweeping up domestic telephone records, but new revelations on the practice sparked a swift backlash.

FBI agents have documented more than two dozen incidents of possible mistreatment at the Guantanamo Bay military base, including a detainee whose head was wrapped in duct tape for chanting verses from the Koran.

US military officials will investigate charges of abuse against terrorist suspects being interrogated at Guantanamo Bay in Cuba, authorities announced.