A source close to former prime minister Dr Mahathir Mohamad’s family confirmed this with FMT, and said that the office raided belonged to Kencana Capital Sdn Bhd, owned by Mokhzani.

The source was not able to provide any information on why the raid was conducted, or how long it lasted.

Mokhzani, Mahathir’s second son, was included in Forbes’ 2017 list of “Malaysia’s 50 Richest”, with a net worth of US$420 million (RM1.8 billion).

He is a founding member of SapuraKencana Petroleum Bhd, and the sole owner of Kencana Capital Sdn Bhd. He was also the chairman of the Sepang International Circuit before stepping down from the post last year.

Mahathir has in the past, claimed that his friends and those thought to be connected to him were being harassed by the government, including through the IRB.

Mahathir, who is now the biggest critic of Prime Minister Najib Razak, also slammed the IRB’s probe on his friend, Lee, saying it showed the “depths to which the government of Malaysia, its prime minister and civil servants have sunk”.

In a letter Lee wrote last May, the businessman claimed he was being investigated under criminal laws instead of civil laws, and that this had caused him to liquidate his assets to settle the income tax bill.

Lee, the executive chairman of Country Heights Holdings Bhd (CHHB), said in the letter: “I would like all my friends to know that I don’t have any personal tax liability. In fact, I have a surplus tax credit with IRB.”

FMT has contacted the IRB and is awaiting a response.