"Mahathir has been admitted to the National Heart Institute for observation for the next few days as advised by the medical team," his office said on Wednesday.

The statement did not provide any details of his symptoms or his condition.

The nonagenarian, who served for more than two decades as prime minister, has a history of heart problems. He has had heart attacks and bypass surgeries.

Mahathir underwent an elective medical procedure in January and was readmitted to the hospital later that month for treatment.

Mahathir and the National Heart Institute did not say at the time what procedure the former leader had undergone, saying only that he had been admitted to the cardiac care unit.

Mahathir served as prime minister for 22 years until 2003. He returned as premier at the age of 92 after leading the opposition coalition to a historic win in 2018, defeating the party that he had once led.

His government collapsed in less then two years due to infighting.

Australian Associated Press