KUALA LUMPUR • Officers from Malaysia's Inland Revenue Board (IRB) raided companies owned by the three sons of former premier Mahathir Mohamad on Tuesday, according to media reports.

Officials at the companies confirmed the raids to Malaysiakini and other news sites.

Kencana Capital, a venture capital firm owned by millionaire businessman Mokhzani Mahathir, was raided on Tuesday, as was Crescent Capital, a venture firm headed by Mr Mirzan Mahathir.

Optics firm Opcom Holdings, founded by politician Mukhriz Mahathir, was also visited by the IRB, with some files taken away.

The raids followed the recent emergence of Tun Dr Mahathir, who was prime minister for 22 years to 2003, as leader of the opposition alliance Pakatan Harapan.

Dr Mahathir is spearheading attacks against Prime Minister Najib Razak over the scandal involving state fund 1Malaysia Development Berhad (1MDB). Datuk Seri Najib was cleared by his attorney-general of any wrongdoing in the scandal.

The US Department of Justice said US$4.5 billion (S$6.1 billion) of 1MDB funds was siphoned out of Malaysia.

Dr Mahathir is under probe by a Royal Commission of Inquiry over the multibillion-ringgit losses incurred by the central bank through foreign exchange trading in the early 1990s. Datuk Mokhzani, listed by Forbes as Malaysia's 34th richest person with a wealth of US$420 million, also has a stake in oil-equipment fabricator Kencana Petroleum.

Datuk Seri Mukhriz is deputy president of opposition Parti Pribumi Bersatu Malaysia headed by his father.

In response to the raids, Dr Mahathir told reporters yesterday that the taxman should also probe PM Najib and his wife over their alleged wealth.