The decision could again reshape politics in the Southeast Asian country less than two years after an alliance of Mahathir, and old rival Anwar Ibrahim, 72, swept out the former ruling party that had been tarnished by corruption scandals.

That former ruling party of six decades, the United Malays National Organisation (UMNO), was among those that had rallied in support of Muhyiddin, along with the Islamist party PAS.

Although Mahathir and Anwar announced on Saturday that they had joined hands again, the palace said in a statement the king made his decision on the basis that Muhyiddin possibly had the support of a majority in parliament.

"His majesty has decreed that the process of appointing a prime minister cannot be delayed," it added. "This is the best decision for all."

Muhyiddin, 72, will be sworn in on Sunday.

"I only ask for all Malaysians to accept the decision announced by the national palace," Muhyiddin told reporters at his home.

Muhyiddin's position could still depend on being able to win a confidence vote in parliament.

The top trending hashtag on Twitter in Malaysia was #NotMyPM.

There was no immediate reaction from Mahathir, who has been interim prime minister since he resigned, or Anwar.

Salahuddin Ayub, a lawmaker from Mahathir and Anwar's political coalition, said they would gather evidence to prove they would be able to form a majority in parliament.

REUTERS