Malaysia's former prime minister Mahathir Mohamad on Monday condemned the questioning of his son by the country's anti-graft agency, calling it "selective" and driven by his political rivalry with the sitting government.

The 98-year-old former two-time leader is a political rival and fierce critic of current Prime Minister Anwar Ibrahim, who came to power in 2022 vowing to stamp out high-level corruption.

Last week the Malaysian Anti-Corruption Commission summoned 66-year-old Mirzan Mahathir, the former premier's eldest son, for questioning over his business activities and to declare all his assets in and outside the country within 30 days.

"As you can see, it is selective. It is all very political. The people who go against the government, will have the law thrown at their face," Mahathir told reporters in Putrajaya city.

"I am worried for him. He has to reveal all transactions since he was 22 years old in 30 days. If he fails, he could face a five-year jail (term)."

The MACC order is part of its probe following revelations contained in the so-called Panama Papers, "as well as his business activities involving the sale and purchase of government-linked companies", it said in a statement last week.

The agency said in August 2022 it started probing "entities linked and named" in the Pandora and Panama papers, which shined a light on tax evasion by the rich and powerful around the world.

Anwar has been accused of using the MACC investigation to go after his political foes.

The move comes after the MACC said it was also investigating Daim Zainuddin, a former finance minister and close ally of Mahathir.