Former Malaysian prime minister Mahathir Mohamad has been admitted to a specialist heart hospital for "observation", a source told AFP Thursday.

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.

He was admitted to the National Heart Institute in Kuala Lumpur on Tuesday, a source close to the former premier said on condition of anonymity without giving further details.

"He is OK and is under observation," the source said.

Another official close to Mahathir said the former leader "is not in any kind of danger. Mahathir is being treated for an infection".

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

He has had numerous heart problems over the years, suffering several heart attacks and undergoing bypass surgery.

Mahathir 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.

He lost in the 2022 general election but has teamed up with Malay-based political parties in an attempt to topple the current government led by Prime Minister Anwar Ibrahim.