The chairman of the Singapore Democratic Party (SDP), Jeffrey George, has been arrested for an alleged drug offence, the Central Narcotics Bureau (CNB) confirmed on Tuesday.
Details of the arrest are sketchy but the police say investigations are ongoing.
Mr Jeffrey, 51 and a shipping engineer, has been chairman of the opposition party since 2013.
He was an election agent for Dr Chee Soon Juan, the SDP secretary general, and John Tan, the party's vice-chairman, in the recent elections in September.
Dr Chee said on Tuesday that the news of Mr Jeffrey's arrest came as a shock to him.
"I have known Jeff for many years and all this time he has discharged his duties as an SDP member and leader with professionalism," Dr Chee told the Straits Times. "He is respected and well liked by his party colleagues."
He added that the family members need support as they go through a difficult period.
"They should be left alone to sort things out," he said.