Police are investigating the Inland Revenue Board for criminal breach of trust over unpaid income tax refunds.

Bukit Aman commercial crimes director Amar Singh confirmed this with the New Straits Times.

The daily reported that former treasury secretary-general Irwan Serigar Abdullah is among those who will be questioned.

Irwan sat on the Finance Ministry's Cash Management Committee, which is alleged to have not allocated sufficient funds to an IRB trust fund meant to facilitate tax refunds.

Finance Minister Lim Guan Eng claimed that in total, RM16 billion in income tax and real property gains tax refunds had been unpaid.

He claimed that as of May 31, the tax refund trust fund only had a balance of RM1.486 billion, which means there is a shortfall of RM14.56 billion.

The unpaid refunds are for 1.6 million taxpayers, comprising of individuals, companies, societies, and foundations, and the cases date back more than six years.

Former prime minister Najib Abdul Razak has called for a Royal Commission of Inquiry into the matter.