Singapore’s anti-graft agency has launched an investigation into a case involving the transport minister, it has been confirmed.

It is a rare high-level probe in a country that prides itself on a government free from corruption.

The Corrupt Practices Investigation Bureau (CPIB) said the minister, S Iswaran, is “assisting” with the inquiry into a case it had uncovered.

“CPIB acknowledges the interest by members of the public in this case because a minister is being interviewed by CPIB,” the bureau said without providing any specifics on what is being investigated.

As investigations are ongoing, it said it is “unable to provide further details”.

“CPIB will investigate this case thoroughly with strong resolve to establish the facts and the truth, and to uphold the rule of law,” it added.

Prime Minister Lee Hsien Loong said he had instructed Iswaran to take a leave of absence until the investigations are completed.

“On 5 July 2023, director CPIB briefed me on a case CPIB had uncovered, and sought my concurrence to open a formal investigation. This would involve interviewing minister S Iswaran, among others,” Lee said in a statement.

“I gave director CPIB my concurrence on 6 July 2023, following which the formal investigation began on 11 July 2023. Minister Iswaran is currently assisting CPIB with the investigations, which are ongoing.

“In minister Iswaran’s absence, senior minister of state Chee Hong Tat will be acting minister for transport.”

Singapore, which has been rocked in recent years by a number of high-profile corruption cases, says it adopts a “strict zero-tolerance approach towards corruption”.

The anti-graft agency said it investigates all cases “without fear or favour” and will not hesitate to take action against any parties involved in corrupt activities.

Iswaran, who has spoken at a number of high-profile shipping events in Singapore, joined Lee’s cabinet as a junior minister in 2006 and held the trade and communications portfolios before becoming transport minister in May 2021.

Graft investigations involving ministers are rare in Singapore. Many cabinet ministers’ annual salaries exceed SGD1m ($750,000) to discourage corruption.

A local law professor told Bloomberg that this is the first graft probe by the CPIB involving a cabinet minister in 37 years.