Newly released Malaysian political heavyweight Anwar Ibrahim said yesterday he expects ex-premier Najib Razak to be jailed over multi-billion-dollar graft claims.

In an interview with AFP a day after he walked free from custody -- where he had languished since 2015 on what supporters say were trumped-up charges levelled at Najib's behest -- Anwar also said he would be back in parliament very soon.

"Give me a few months, I should be back as an MP. It is the correct thing to do," he said.

Anwar's release on Wednesday capped an astonishing week in Malaysian politics that saw Najib's long-ruling Barisan Nasional coalition booted from power in a revolution at the ballot box.

The election dramatically reversed Anwar's fortunes, from prisoner to presumptive successor to 92-year-old Prime Minister Mahathir Mohamad.

It also imperilled Najib, who Anwar said now faces an "arduous" legal battle -- without the protection of high office.

Accused of overseeing the plundering of state fund 1MDB, Najib's position has looked increasingly precarious. Police carried out extensive searches of his home overnight.

Anwar predicted that Najib would likely take up the spot he had just vacated in prison. "He will certainly be charged," he said.

Anwar, 70, declined to say how he thought Najib's case would play out, as it depended on "how he can defend himself in court".

But Anwar added: "It will be very difficult for him to escape (going to) prison."

Najib and 1MDB deny any wrongdoing.

Mahathir, who came out of retirement to lead the revolt against Najib, has signalled he will hand power to Anwar within two years.

The younger man's return to politics has been the subject of much speculation and he confirmed he would be seeking to return as an MP soon -- but would not seek a position on the front benches just yet.

"I am not intending to join the cabinet," he said he had told Mahathir.

Anwar and Mahathir, who previously led Malaysia as premier from 1981-2003, have a stormy relationship that has dominated Malaysian politics for decades.

Anwar enjoyed a meteoric rise in the now-ousted Barisan Nasional and was heir-apparent to the premiership until he fell out with Mahathir in the 1990s and was sacked.