Malaysia’s new leader, Mahathir Mohamad, said he barred his scandal-tainted predecessor and wife from leaving the country to prevent them from fleeing from possible prosecution over a huge corruption scandal.

Mahathir, who also took the significant step of appointing an ethnic Chinese as finance minister, said on Saturday that Najib Razak would “face the consequences” if any wrongdoing was found by investigators.

“There are a lot of complaints against him, all of which have to be investigated,” Mahathir told a news conference. “We have to act quickly because we don’t want to be saddled with extradition from other countries.”

Mahathir said that there was sufficient evidence to investigate Najib over the corruption scandal involving the1MDB state fund that is being investigated in the United States and other countries. US investigators say Najib’s associates stole and laundered $4.5bn from the fund, with some $700m landing in Najib’s bank account and around $30m used to buy jewellery for his wife. Najib has denied any wrongdoing.

A leaked flight manifesto had revealed that Najib and his wife Rosmah Mansor were planning to take a private jet to Indonesia on Saturday, fuelling rumours that he was bolting the country days after a shoching electral defeat that ended his coalition’s 60-year grip on power.

Najib responded on Saturday that he respected the travel ban and would remain in the country with his family. He also said he was committed to “facilitating a smooth transfer of power”.

Mahathir’s decision to ground Najib fulfils an election promise, as does his appointment of an ethnic Chinese as finance minister, the first ethnic minority to hold the powerful post in 44 years.

The appointment of Lim Guan Eng, a chartered accountant who led the wealthy northern state of Penang since 2008, reflects reforms promised by Mahathir’s alliance to heal racial divisions in the country blamed on decades-old preferential policies. The finance post has been held by a Muslim Malay since 1974.

“I don’t consider myself as a Chinese, I am a Malaysian. I will ensure that the interests of all Malaysians are protected,” Lim, 57, said at a news conference.

Lim and Mahathir have a long and checkered history: he was a bitter foe of Mahathir during the older man’s earlier 22-year stint as prime minister and was thrown in jail twice. Lim was jailed during a political crackdown in October 1987 that Mahathir said was aimed at preventing racial riots, and again in 1998 under the Sedition Act.

But on Saturday, a smiling Lim stood by 92-year-old Mahathir as his appointment was announced.

In addition to naming Lim Guan Eng, Mahathir also named former deputy prime minister Muhyiddin Yassin as home affairs minister and Mohamad Sabu as defense minister.

Mahathir said his cabinet would have 25 members and that he would name the remaining members this coming week. His deputy is Wan Azizah Wan Ismail, the country’s first female deputy prime minister and head of another party in the pact.