A Singapore government minister and a property tycoon were arrested this week, the anti-graft body said on Friday, without giving details of what prompted the rare high-level probe that has gripped the city state.

Transport Minister S. Iswaran and managing director of Hotel Properties Ong Beng Seng were arrested on Tuesday and subsequently released on bail, the Corrupt Practices Investigation Bureau (CPIB) said in an emailed response to a Reuters query.

The CPIB said on Wednesday that it had launched an investigation into Iswaran.

The case is rare in Singapore, a top Asian financial hub that prides itself on a corruption-free government. Cabinet ministers are paid handsomely to discourage graft, with some ministers’ annual salaries exceeding S$1 million ($758,000).

Ong is known for bringing Formula One races to the city-state and his company said he is cooperating with the anti-graft agency.

Iswaran’s passport has been impounded, but the CPIB allowed Ong to travel out of Singapore on Friday.

“CPIB assessed and acceded to Ong’s request to travel overseas. Ong’s bail quantum was also increased to S$100,000. Upon his return, Ong is required to report to CPIB and surrender his passport to the bureau,” said the anti-graft body.

The Singapore-listed Hotel Properties Ltd (HPPS.SI) said in a statement no charges had been filed against Ong, adding that he was asked by the CPIB to provide information on his interactions with the transport minister.

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

The Prime Minister’s Office said on Thursday that Iswaran was not allowed to leave Singapore during the investigation and he would have no access to any official resources or government buildings, local media reported.

The 79-year-old Ong’s company has around 38 hotels and resorts operating under brands that include COMO, Four Seasons, Hard Rock Hotels and Concorde, according to the London Stock Exchange’s Refinitiv Eikon.

Shares in Hotel Properties Ltd fell as much as 7% on the news and were last down 4.4%, heading for their worst session in more than two years.

Malaysia-born Ong and his wife, Christina, had a net worth of $1.75 billion in 2022, according to Forbes.

($1 = 1.3185 Singapore dollars)