Malaysia's 92-year-old new leader Mahathir Mohamad said he expects to stay as prime minister for up to two years and vowed not to cut any deals to keep his predecessor out of jail for alleged corruption.

Mahathir told the Wall Street Journal he would be in power for one to two years -- before an expected handover to former opposition leader Anwar Ibrahim, who is expected to be released on Wednesday after three years in jail on a sodomy conviction.

Mahathir -- who ruled Malaysia from 1981-2003 -- came out of retirement to oust scandal-tainted former premier Najib Razak in an astonishing election turnaround last week.

Mahathir was asked in an interview by video link whether a deal could be cut with Najib, who is alleged to have overseen the looting of government investment fund 1MDB.

"No deal," Mahathir said in the interview, conducted for a business forum organised by the newspaper in Tokyo.

Billions of dollars are believed to have been siphoned off from the fund, with most reportedly disappearing overseas, while $681 million also mysteriously appeared in Najib's personal bank accounts in 2013.

"We are now in process of getting into details of matters he suppressed in his time," Mahathir said of Najib.

Without a deal to help recover the funds, Najib faces the likelihood of prosecution and possible criminal charges. Mahathir has ordered him barred from leaving the country.

Anwar, whose sodomy conviction is believed by supporters to have been concocted by Najib to derail the opposition, is expected to be pardoned by the country's king on Wednesday and released.

Mahathir has previously said he expects to stay in charge for a period of time, partly to ensure a smooth transition, but has already signalled he would eventually yield to Anwar.