The Department of Justice on Monday appointed a special prosecutor to pursue an investigation into Alberto Gonzales, former attorney-general, and other former White House officials, raising the spectre of criminal charges against a close ally of President George W. Bush.

The move by Michael Mukasey, the current attorney-general, followed the release of a scathing report by the inspector-general of the justice department, which found that Mr Gonzales had abdicated his responsibility when he oversaw the “arbitrary” removal of nine US attorneys in 2006.