Najib Abdul Razak may have repeatedly insisted that he is only an advisor to 1Malaysia Development Berhad but former premier Dr Mahathir Mohamad has insisted the prime minister is responsible for calling the shots in the debt-ridden company.

Mahathir said it was unlikely that the management of 1MDB dared to defy the company's advisor, who is also the prime minister and finance minister.

He added whatever Najib "advised" was ultimately a directive.

"It is inexcusable that the management which is appointed by the prime minister would reject his advice.

"So like the British advisor of old, the advice of the advisor is a directive.

"Since then, three CEOs of 1MDB have resigned without explanation. Could it be because they could not accept the advice?" said Mahathir in his latest blog posting today.

Najib leads the 10-member advisory board to 1MDB which comprise eminent international figures.

The finance ministry-owned 1MDB has been embroiled in controversy as it struggles to pay off its massive RM42 billion debt.

[More to follow]