Anwar Ibrahim sworn in as Malaysian PM

Malaysia's Anwar Ibrahim has been sworn in as prime minister, capping a three-decade political journey from a protege of veteran leader Mahathir Mohamad to protest leader, a prisoner convicted of sodomy and opposition leader.

His appointment on Thursday ends five days of unprecedented post-election crisis, but could usher in a new instability with his rival, former prime minister Muhyiddin Yassin, challenging him to prove his majority in parliament.

Both men failed to win a majority in a Saturday election, but the constitutional monarch, King Al-Sultan Abdullah, appointed Anwar after speaking to several MPs.

Anwar takes over at a challenging time: the economy is slowing and the country is divided after a tight election that pitted Anwar's progressive coalition against Muhyiddin's mostly conservative ethnic-Malay, Muslim alliance.

The 75-year-old Anwar has time and again been denied the premiership despite getting within striking distance over the years: he was deputy prime minister in the 1990s and the official prime minister-in-waiting in 2018.

In between, he spent nearly a decade in jail for sodomy and corruption in what he says were politically motivated charges aimed at ending his career.

The uncertainty over the election threatened to prolong political instability in the Southeast Asian country, which has had three prime ministers in as many years, and risks delaying policy decisions needed to foster economic recovery.

Anwar told Reuters in an interview before the election that he would seek "to emphasise governance and anti-corruption, and rid this country of racism and religious bigotry" if appointed premier.

His coalition, known as Pakatan Harapan, won the most seats in Saturday's vote with 82, while Muhyiddin's Perikatan Nasional bloc won 73. They needed 112 - a simple majority - to form a government.

The long-ruling Barisan bloc won only 30 seats - the worst electoral performance for a coalition that had dominated politics since independence in 1957.

Barisan said on Thursday it would not support a government led by Muhyiddin, though it did not make any reference to Anwar.

Muhyiddin, after Anwar's appointment, asked Anwar to prove his majority in parliament.

Muhyiddin's bloc includes the Islamist party PAS, whose electoral gains raised concern among members of the ethnic Chinese and ethnic Indian communities, most of whom follow other faiths.

The decision on the prime minister came down to King Al-Sultan Abdullah, after both Anwar and Muhyiddin missed his Tuesday afternoon deadline to put together a ruling alliance.

The constitutional monarch plays a largely ceremonial role but can appoint a premier he believes will command a majority in parliament.

Malaysia has a unique constitutional monarchy in which kings are chosen in turn from the royal families of nine states to reign for a five-year term.

As premier, Anwar will have to address soaring inflation and slowing growth as the economy recovers from the coronavirus pandemic, while calming ethnic tensions.

The most immediate issue will be the budget for next year, which was tabled before the election was called but has yet to be passed.

Anwar will also have to negotiate agreements with MPs from other blocs to ensure he can retain majority support in parliament.