Ex-premier Najib Abdul Razak has hit back at Dr Mahathir Mohamad for saying that he was “confused and concerned” over the plea bargain for his stepson Riza Abdul Aziz’s money laundering charges.

In a sarcastic and hard-hitting post that is likely to escalate the war of words between the two former prime ministers, Najib defended Riza's track record and took a veiled swipe at corporate deals which involved Mahathir's sons.