Parti Pejuang Tanahair founder Dr Mahathir Mohamad has questioned a Court of Appeal's decision to temporarily return former premier Najib Razak's passport and allow the latter's trip to Singapore.

Claiming the move was extraordinary, Mahathir described Najib as Malaysia's first "VIP criminal" who was given special treatment, including being granted leave from court after citing health reasons but was seen at another location.