Former Malaysian premier Najib Razak yesterday quit as head of the country's largest party Umno, just hours after he was put on an immigration blacklist that barred him from leaving the country.

His resignation from Umno, and from the chairmanship of Barisan Nasional - the coalition that Umno leads - was to be expected after BN suffered a massive election defeat on Wednesday. Being grounded, however, was largely due to his nemesis and new Prime Minister Mahathir Mohamad.

"It's true, I prevented Najib from leaving the country," Tun Dr Mahathir said yesterday. He explained that Datuk Seri Najib was prevented from going abroad because "there's sufficient evidence that certain things done by the former PM" require an investigation.

Mr Najib has been linked to the money-laundering allegations surrounding state fund 1MDB after RM2.6 billion (S$880 million) was found in his personal accounts.

He has said the funds were a donation from the Saudi royal family and been cleared by Malaysian authorities of any wrongdoing. Said Dr Mahathir: "We have to act quickly because we don't want the problem of extradition with other countries."

Dr Mahathir was speaking at a press conference to name three senior figures to the Cabinet. Democratic Action Party chief and outgoing Penang chief minister Lim Guan Eng will be Finance Minister, Parti Amanah Negara president Mohamad Sabu will be Defence Minister, and Parti Pribumi Bersatu Malaysia president Muhyiddin Yassin, Home Affairs Minister.

Tan Sri Muhyiddin was Mr Najib's former deputy who was sacked when he spoke out on 1MDB.

Notably absent was Deputy PM and Parti Keadilan Rakyat (PKR) leader Wan Azizah Wan Ismail. Hours later, it emerged all was not well at the consensus-ruled Pakatan Harapan coalition. PKR vice-president Rafizi Ramli wrote on his blog that discussions are still ongoing and the naming of the ministers was not final until agreed upon by all four parties in the PH coalition.

He added that Dr Mahathir would discuss the appointments with Datuk Seri Anwar Ibrahim, the jailed de facto leader of PKR who is due to be given a royal pardon by the King and released on Tuesday.

Dr Mahathir has promised to hand over the PM position to Mr Anwar once he is eligible to contest in a by-election and becomes an MP.

In stark contrast to Mr Anwar's impending return, Mr Najib's political future looked bleak.

The embattled former premier told a press conference yesterday: "Umno and BN were defeated badly so I, as Umno president and BN chairman, will step down." He said former deputy prime minister Ahmad Zahid Hamidi will take over as BN chairman and Umno president, while former defence minister Hishammuddin Hussein will take on the duties of deputy Umno president and deputy BN chairman.

The press conference capped a dramatic day for Mr Najib. A flight manifest on social media showed he and his wife Rosmah Mansor were planning to travel to Indonesia, prompting dozens of journalists and an angry mob to gather at Subang Airport early in the morning.

But before the couple could get on the private flight scheduled to depart at 10am, the travel ban was issued.

Dr Mahathir made clear he would keep up the pressure. Last night, Reuters reported that Malaysian police had raided apartments linked to Mr Najib's family.