Malaysia's former prime minister Mahathir Mohamad was questioned yesterday by the police for the second time in four months in connection with his continued criticism of Prime Minister Najib Razak over alleged financial mismanagement at state investment firm 1MDB, and revelations that millions of dollars had been deposited into the Prime Minister's bank account.

"I feel intimidated, of course. But in exercising my right to speak, I'll continue to speak," Tun Dr Mahathir told a news conference yesterday evening.

Police spent over an hour at his office in Putrajaya, asking questions about a recent blog post he published regarding the Attorney-General's investigation into the US$681 million (S$958 million) found in Mr Najib's account, a sum that was tagged as a "donation" by the Malaysian Anti-Corruption Commission.

The anti-graft agency said yesterday that a review panel had asked it to continue investigations into the funds received by Mr Najib, despite an order by the Attorney-General to close the case.

Dr Mahathir said he refrained from answering all the questions posed by the police, reserving his responses for a court hearing, if there is one. Police are investigating Dr Mahathir for criminal defamation of Attorney-General Mohamed Apandi Ali after reports were lodged against the 90-year-old.

Last November, police questioned Dr Mahathir over his remarks at an anti-government rally in August.

Another Umno bigwig turned staunch critic of Mr Najib, deputy Umno president Muhyiddin Yassin, also appears to be on shaky ground. Tourism and Culture Minister Nazri Aziz has stated that he would propose to Umno that Tan Sri Muhyiddin be suspended from his post, The Malay Mail Online reported. Mr Muhyiddin was sacked as deputy prime minister last July.

As Mr Najib continues to ignore his critics and solidify his power, Dr Mahathir is appealing to politicians from both sides of the divide.

"This is a problem affecting the nation… Now is the time to act as citizens without party affiliation or loyalty," Dr Mahathir said yesterday.

"I think I have to make it clear to Najib that it's not just me, but there are lots of people, citizens, concerned with his kind of administration that's based on 'cash is king'."