Indian-origin Minister S Iswaran, under fire over a corruption scandal, was questioned for around 10 hours by the authorities, according to local media reports.
Iswaran, 61, arrived at the Corrupt Practices Investigation Bureau (CPIB) building at Lengkok Bahru in Redhill estate at about 10.50 am on Tuesday and left at 8.48 pm in an SUV, according to a report by TODAY newspaper.
The minister, who has taken a leave of absence from his official duties, entered the compound alone.
Iswaran and Hotel Property Limited Managing Director Ong Beng Seng were arrested on July 11, the anti-graft body said last week, adding that the two were assisting with investigations. The agency did not give details on the nature of the probe.
Both were released on bail, and their passports were impounded as part of their bail conditions.
Prime Minister Lee Hsien Loong instructed Iswaran to take a leave of absence until the investigation was completed, the Prime Minister's Office said last week.
He will remain in the city-state during this period and have no access to official resources and government buildings, the Straits Times newspaper reported.
Ong, 77, is a Malaysian based in Singapore and owns the rights to the Singapore Grand Prix and is chairman of race promoter Singapore GP.
He returned to Singapore from Bali on a private plane on Monday afternoon after being allowed by the CPIB to travel overseas. He left for the Indonesian resort island last Friday after posting bail of SGD 100,000.
Iswaran and Ong are known to be key figures in making Singapore's pitch to become a part of the Formula One circuit.
Ong is chairman of the Singapore Grand Prix, which annually organises the F1 night race at the Marina Bay Street Circuit.
In the mid-2000s, Iswaran, a junior trade minister at the time and Ong convinced then Formula One Group Chief Executive Bernie Ecclestone to make Singapore the venue for the sport's first night race, starting in 2008.
Iswaran reportedly knew Ong when he was a bureaucrat and top executive at Temasek, according to the report.
The minister's political career spans more than 26 years since he was first elected in 1997 as a Member of Parliament for West Coast Group Representation Constituency (GRC).
Before being appointed to the Cabinet in 2006, he was on several government parliamentary committees and was the deputy speaker of Parliament from September 2004 to June 2006.
He has been Minister for Transport since May 2021 and has been concurrently minister-in-charge of trade relations at the Ministry of Trade and Industry (MTI) since May 2018.