Has the taxman ever paid a visit to Prime Minister Najib Abdul Razak?

That's the question posed by former prime minister Dr Mahathir Mohamad, who wants to know how much the Inland Revenue Board has collected from Najib.

"The income tax people are always on the lookout for people who live beyond their means. They would raid these people and would force them to pay additional tax, should they feel that the culprits have not paid up fully on their wealth.

"But of late, we see some selectivity in the focus of the income tax people," Mahathir ( photo ) wrote in his blog today.

He said Najib's wealth has been attributed to business interests, which meant the prime minister would have to pay additional income taxes

"If he made so much money from business, he should have paid income tax. Have the income tax people investigated him regarding his business profits?

"How much tax has he paid? It is a secret of course. But I hope it is not a cover-up," Mahathir added.

How about Riza Aziz and Jho Low?

Mahathir said others who might have escaped the Inland Revenue Board's scrutiny include Najib's stepson Riza Aziz ( photo ), and 1MDB-linked business tycoon Jho Low.

"(Riza) is reported to have spent hundreds of millions of US dollars or ringgit buying luxury residences in London, New York and Hollywood. He also expended many millions to finance the production of the film 'The Wolf of Wall Street'.

"Then there is Jho Low. He bought a bank for 260 million US dollars. Where did he get the money. Is it borrowed? Did he sell the bank and paid taxes on the profit.

"He also bought luxury flats in New York and Hollywood. Where did the hundreds of millions he paid for all these come from? Has he paid tax on them?

"I believe executives of 1MDB and its subsidiaries are paid high salaries. Have they paid taxes on their earnings?" Mahathir asked.

He was referring to Riza's alleged purchase of homes in the US and England, including a RM110 million apartment in New York.

Low ( photo ), whose real name is Low Taek Jho, meanwhile, is alleged to have used 1MDB funds to buy out UBG bank.

Mahathir's comments come as reports emerge claiming that almost US$700 million was deposited in Najib's personal bank accounts.