Former inspector-general of police Musa Hassan has threatened to sue blogger Raja Petra Kamaruddin for defamation if he does not retract his allegation that the ex-top cop was part of a plot to jail Anwar Ibrahim.

"I feel this is unprincipled slander that is not factual.

"The case has been tried in court, and there has been no legal challenge on allegations of (Anwar being) fixed," he told a press conference in Petaling Jaya today.