Former Malaysian prime minister Najib Razak said on Saturday he was going to take a "short break" after his election loss, as an angry crowd descended on an airport amid speculation he would fly out of the country.
Dr Mahathir said he was instructing the auditor-general to remove any restrictions on publicising the details of a report from a local investigation into 1MDB, and planned to replace the attorney-general who helped Mr Najib keep the investigation contained, though he did not name a candidate for the role.
The defeat of Najib's Barisan Nasional (BN) coalition in last week's poll by an alliance led by his one-time mentor Mahathir Mohamad was a political quake, which toppled an increasingly authoritarian regime that had ruled the country for six decades.
He re-entered politics after being angered by a corruption scandal in which associates of Mr Najib were said to have taken £3.7billion from a state fund.
Najib has consistently denied any wrongdoing in connection with 1MDB.
Possible return of Anwar Ibrahim: Mahatir said after his victory over Najib that the country's monarch had agreed to pardon jailed opposition politician Anwar Ibrahim, who has been serving a jail sentence since 2015 on "sodomy" charges that Anwar says were politically motivated.
It came a day after the 92-year-old was sworn in after a shock win that toppled the country's long-ruling coalition.
Mahathir was a maverick Malay nationalist in the early days of his political career who survived expulsion from the dominant United Malays National Organization party, and became the first commoner prime minister of Malaysia.More news: Oil prices near multi-year highs as Iran sanctions tighten supply outlook
We will remind, on may 9 in Malaysia's parliamentary elections were held.
Mahathir is now the world's oldest elected leader and, analysts say, seems intent on using what may be the final chapter of his life to clean up Malaysia - he called it a "mess" - and fashion a more positive legacy.
USA investigators say Najib's associates stole and looted $4.5 billion from the fund, with some $700 million landing in Najib's bank account and around $30 million used to buy jewelry for his wife.
Najib's remark then drew an immediate response from PM Lee, who said that this is "because you have confidence in the result", which saw the two leaders laughing.
Mahathir's victory upended six decades of control by the Barisan Nasional coalition, which he himself formerly headed as Malaysia's Prime Minister from 1981 until 2003.
Mahathir has said he will step aside and hand over the prime minister's post to Anwar once he is pardoned.
U.S. investigators said Najib's associates stole $4.5bn from the fund, of which some $700m landed in Najib's bank account, and some $30m was used to buy jewellery for his wife.
Asked about 1MDB on Friday, Mahathir accused Attorney-General Mohamed Ali Apandi - who cleared Najib over the scandal - of having "undermined his own credibility".
"There is sufficient evidence that an investigation into certain things. done by the former prime minister has to be done and, if necessary, the rule of law will apply", he said.