Former prime minister Dr Mahathir Mohamad is open to Najib Abdul Razak coming back on as prime minister - only if there is proof of no wrongdoing in 1Malaysia Development Bhd (1MDB).

However, Mahathir said, Najib must first resign to allow a full investigation into the 1MDB finances.

"If no crime can be detected and all the money is returned, Najib can come back as prime minister and lead BN in the next election," Mahathir said in a blog posting today.

Otherwise, the truth about 1MDB would not surface, said Mahathir.

"As long as the prime minister is there, no proper investigation can be made.

"Already we are seeing not only are reports to the police on 1MDB and Jho Low not being investigated, but the person who made the report being declared a bankrupt, his house confiscated and sold and he himself being investigated for money laundering and financing terrorists.

Mahathir was referring to his loyalist, sacked Batu Kawan Umno vice-chief Khairuddin Abu Hassan ( photo ), who had lodged police reports against 1MDB.

The former prime minister also pointed out despite the government's efforts to punish him, the courts have declared that he is not bankrupt.

'I tried to resolve the problem privately...'

Mahathir also defended his attacks against Najib, stating that he had tried to resolve the problem with the prime minister privately, but to no avail.

"So I had to go public. Najib has destroyed Umno and BN. I know he will lose the next election.

"And then the whole country will see turmoil as no party, will have the majority to run the country," he said.

Furthermore, he said, Pakatan Rakyat is also in disarray and without any strong coalition to lead the country, it would fall into turmoil.

"The opposition cannot, because the parties will be quarrelling among themselves. A Pakatan government will be weak and unstable.

"Without a strong government, this country will become anarchic. The crisis that will accompany the anarchic situation will be worse.

"So I decided to expose the wrongdoings of 1MDB, in which the prime minister is effectively the head," Mahathir said.