President George W. Bush’s nominee to become US attorney-general faced sharp criticism from Democrats on Thursday for refusing to rule out use of a controversial interrogation technique that simulates drowning.

Michael Mukasey, a retired federal judge, picked by Mr Bush to become the administration’s top legal officer, said it was unclear whether the technique, known as waterboarding, represented torture. Waterboarding is rumoured to be used by the US to interrogate suspected terrorists since the attacks of September 11 2001, although the Bush administration has never confirmed it.