PETALING JAYA (THE STAR/ASIA NEWS NETWORK) - Former Malaysian prime minister Najib Razak has been slapped with an extra tax bill of RM1.5 billion (S$498 million) by the Inland Revenue Board (IRB), The Edge reported on Monday (April 1).

The financial daily reported that the IRB had sent a letter to Najib about a week ago, stating the extra tax he had to pay for the years 2011 to 2017.

Quoting sources, the report said the amount is on top of what he had already paid based on his declared income for the seven years.

Based on IRB's assessment, Najib had not declared taxable income of close to RM4 billion during that period, and this included the RM2.6 billion "donation" that he purportedly received from the Saudi Arabian government.

The Edge also quoted tax experts saying donations are subject to income tax, and Najib have committed an offence by not declaring the alleged RM2.6 billion donation as his income, regardless of the source.

But Najib has claimed that funds received from abroad is not taxable in Malaysia.

He said in a Facebook posting on Monday that the Pakatan Harapan government had previously accused him of receiving billions in funds from foreign sources, but insisted that such funds are not be subject to taxes.

"Firstly, political contribution including from the Saudi Arabia Ministry of Finance is not subject to tax under the law.

"Secondly, as is publicly known, income obtained from abroad are not taxable under taxation laws," he wrote.

Najib, 66, last year said in a TV interview that he did not verify the source of the RM2.6 billion that ended up in his bank account, and that he had assumed those to would be donations linked to Saudi Arabia.

His trial over funds allegedly received from SRC International, formerly a unit of 1MDB, will start on Wednesday (April 4).