Malaysia's new leader, Mahathir Mohamad, said Saturday that defeated scandal-tainted prime minister Najib Razak and his wife have been barred from leaving the country to prevent them from fleeing from possible prosecution over a massive corruption scandal.

A leaked flight manifesto showed that Najib and his wife, Rosmah Mansor, were due to leave on a private jet on Saturday to Indonesia's capital, Jakarta, fuelling rumours that he was bolting the country after a shocking electoral defeat earlier in the week that ended his coalition's 60-year grip on power.

Najib had said in a statement on social media on Saturday that he was planning to take a short vacation to spend time with his family. The immigration department, which initially said there was no travel ban, later issued a statement to say Najib and his wife had been blacklisted from leaving the country.

Mahathir confirmed that he prevented Najib from leaving. He said there was sufficient evidence for an investigation into Najib, in reference to the massive corruption scandal involving the 1MDB state fund that Najib set up and is being investigated in the United States (US) and other countries.

US 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 $30m used to buy jewellery for his wife. Najib has denied any wrongdoing.

“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 the investigations would take some time because investigators need to contact authorities in other countries and gather evidence. He has said Najib will have to face a court if any wrongdoing is found.

Najib responded swiftly, saying he respects the immigration department's ruling and will remain in the country with his family. He also said he was committed to “facilitating a smooth transfer of power.”

Later Saturday, Najib said at a news conference that he was stepping down as president of the United Malays National Organization and as chairman of the National Front coalition to take responsibility for Wednesday's election defeat.

The announcement came after strong calls emerged from the UMNO, the linchpin of the coalition, for Najib to resign.

The National Front, which has ruled Malaysia since independence from Britain, won only 79 of the 222 parliamentary seats, losing power to Mahathir's four-party alliance amid public anger over the 1MDB scandal and a rising cost of living.

It was a remarkable comeback for the 92-year-old Mahathir, who was prime minister for 22 years until his retirement in 2003.

Najib, 64, said his deputy, Ahmad Zahid Hamidi, would take over as UMNO president.

“We accept the people's verdict with an open heart,” Najib said. “Maybe this will be an opportunity for us to fix our weaknesses and shortcomings, although these are more a matter of perception than reality. God willing, UMNO will continue to live.”

Amid the 1MDB scandal, Najib sacked critics in his government, including an attorney general and a deputy prime minister, and muzzled the media.

The subsequent attorney general, Mohamed Apandi Ali, cleared Najib in 2016, saying that the money was a donation from the Saudi royal family and that most of it was returned.

Mahathir has indicated that Mohamad Apandi could be dismissed for hiding evidence of wrongdoing.

Also Saturday, Mahathir appointed Lim Guan Eng, an ethnic Chinese, as finance minister, the first ethnic minority to be appointed to the powerful post in 44 years.

He also named former Deputy Prime Minister Muhyiddin Yassin as home affairs minister and Mohamad Sabu as defense minister.

The three are party leaders in his alliance.

Since 1974, the finance minister had been an ethnic Muslim Malay.

The appointment of Lim, a chartered accountant who led the wealthy northern state of Penang since 2008, reflects reforms pledged by Mahathir's alliance to heal racial divisions in the country blamed on decades-old preferential policies.

Mahathir said he would name the rest of his 25-member Cabinet this coming week.