Malaysian former prime minister Mahathir. Photo: Xinhua

A staunch Muslim nationalist backed by a scandal-mired party was sworn in as Malaysia's Prime Minister Sunday after a reformist government's collapse, but ex-leader Mahathir Mohamad, 94, slammed the move as illegal.

The Southeast Asian nation was plunged into turmoil after Mahathir's "Pact of Hope" alliance, which stormed to a historic victory in 2018, collapsed amid bitter infighting.

He lost in a power struggle however to little-known Muhyiddin Yassin, who heads a coalition dominated by the multi-ethnic country's Muslim majority and has faced criticism for controversial remarks about race.

The King's decision Saturday to pick Muhyiddin as prime minister was greeted with shock as Mahathir's allies claimed to have enough support, and it sparked widespread anger that the democratically elected government had been thrown out.

Muhyiddin's coalition includes the United Malays National Organisation (UMNO), the party of disgraced ex-leader Najib Razak, , as well as a hardline group that wants tougher Islamic laws.

UMNO was the corruption-riddled lynchpin of a coalition thrown out at the 2018 elections amid allegations Najib and his cronies looted billions of dollars from state-fund 1Malaysia Development Berhad (1MDB) - an insolvent Malaysian strategic development company. Najib is now on trial for corruption.

Just before Muhyiddin's inauguration, Mahathir accused him of betrayal and said he would seek a parliament vote challenging the new leader's support.

Despite a last-minute bid by Mahathir to prove that he had enough support to return as prime minister, Muhyiddin's inauguration went ahead Sunday at the national palace.

His alliance boycotted the ceremony.

To become prime minister, a candidate must prove to the King, who appoints the prime minister, that he has the backing of at least 112 MPs.

AFP