Malaysia's Prime Minister Anwar Ibrahim refused to answer questions on Tuesday on the existence of a royal decree that would allegedly allow jailed former premier Najib Razak to serve his prison sentence at home.

Malaysia's jailed ex-leader Najib Razak will begin his defence this week against graft charges tied to more than $500 million in alleged bribes, and argue to serve the rest of his sentence under house arrest.

Malaysia Edition helps you connect the dots on the biggest stories playing out in Malaysia every week. Sign up here to get the newsletter in your inbox. Whether former prime minister Najib Razak is entitled to serve the rest of his halved jail sentence on house arrest instead of in prison is a widely-discussed issue,