Former Malaysian prime minister Mahathir Mohamad was discharged from a specialist heart hospital on Friday, a source told AFP, after four days of medical checks.

The 98-year-old former leader is one of Malaysia's most dominant political figures, having served twice as prime minister for a total of 24 years.

Mahathir had been admitted to the National Heart Institute in Kuala Lumpur on Tuesday for "observation", according to the source, an aide close to the former premier who spoke on condition of anonymity.

"Yes, Mahathir has been discharged from the hospital," they said on Friday, without giving further details.

Another official close to Mahathir said on Thursday that the former leader was "being treated for an infection".

Mahathir has suffered several heart problems in recent years, including at least two heart attacks, and has undergone at least two bypass surgeries.

He was also admitted to hospital in December 2021 and January 2022 for several days to undergo medical checks.

He led Malaysia from 1981 to 2003 and then returned to power in 2018 at the age of 92, heading a reformist coalition.

That administration collapsed in 2020 due to infighting.

Mahathir lost in the 2022 general election but has teamed up with ethnic Malay political parties in an attempt to unseat the current government, led by Prime Minister Anwar Ibrahim.