Pointing out that alleged financial wrongdoings during Dr Mahathir Mohamad's tenure were not probed, a minister outlined the difference between the former premier and current number one Najib Abdul Razak.

Tweeting on the matter, Abdul Rahman Dahlan said Mahathir's "financial mistakes" were known during his time.

"Yes true. But under Najib it (the allegations) is investigated," tweeted the housing, local government and urban well-being minister.

"Najib has asked the AG (auditor-general), the PAC (Public Accounts Committee) to investigate 1MDB," he added referring to 1Malaysia Development Bhd, which is being targeted by Mahathir.

Mahathir had on Thursday criticised Najib and raised the murder of Altantuya Shaariibuu as well as the 1MDB isssue.

Mahathir also said Najib had failed to give convincing explanations on the state investment fund.

The former prime minister further said Umno and BN would lose the next general election if Najib remained as prime minister.

Mahathir dealt another blow yesterday, saying a prime minister must be seen to be clean and able to answer questions.

"Najib cannot even answer and has not answered any question, beyond exercising elegant silence or saying the allegations are not true," he added.

During his 22-year reign, Mahathir had been accused of numerous wrongdoings ranging from corruption to abuse of power.