Amanah vice-president Mahfuz Omar, who described himself as Najib Abdul Razak’s senior at Kajang prison, is also demanding answers from the government over an anonymous message claiming that the former premier has been accorded certain privileges.

Calling on the authorities to treat all prisoners in the same manner, he said: “I was imprisoned in Kajang myself. I am more senior than Najib in Kajang but I did not get any special treatment.”...