Dr Mahathir Mohamad has now broadened his attack to include Prime Minister Najib Abdul Razak's entire cabinet.

The former premier said the ministers appear to be incapable in tackling the 1MDB issue.

"What appears to be obvious is that the whole cabinet seems to be unable to deal with this problem.

"Some appear not to understand. Others feel it is none of their business. Others think it is safer not to say anything.

"So each one of them go about their own business and they behave accordingly," he told reporters in Kuala Lumpur today, when asked which minister should quit over their own ineptitude.

Quizzed if Deputy Prime Minister Muhyiddin Yassin should quit, Mahathir said it is up to him whether to resign or to stay in the cabinet and maintain close communication with Najib.

Muhyiddin had previously been caught on video criticising 1MDB at a closed-door function with Umno members.

He was also not present at the cabinet meeting where Najib issued an ultimatum to his ministers.

On Monday, Utusan Malaysia quoted sources saying that Najib had issued an ultimatum that cabinet members who disagree with him on the 1MDB issue should resign, just as Second Finance Minister Ahmad Husni Hanadzlah unveils a restructuring plan for the state investment fund.

Defence Minister Hishammuddin Hussein quickly tweeted that he conditionally supports Najib's ultimatum.

However, Culture and Tourism Minister Nazri Abdul Aziz later told Malaysiakini that it was not an ultimatum and the atmosphere of the meeting was not tense either.

Instead, Nazri said the prime minister merely told his cabinet that it needs to stand together on the 1MDB issue and if any of the cabinet members are uncomfortable with this, he would understand if they opted to resign.

Related stories

1MDB's 'tell all' raises more queries, say critics

1MDB reveals all on 'missing' billions

Special meet was on 1MDB, 'doable' plan revealed

Bank Negara commences formal inquiry on 1MDB

Shafie: Why should I quit for asking questions?

'Arrived late' Muhyiddin skips special meet

Dr M has good reasons to doubt auditor-general