The police arrested 61 foreign nationals in the forested areas along Punggol on Friday night for being allegedly involved in illicit activities.
Police said in a statement on Saturday that the suspects, comprising men and women, are "believed to have used the cover of the forest for various illicit activities such as vice and gambling".
In the raid, which involved officers from the Ang Mo Kio Police Division, Criminal Investigation Department and Gurkha Contingent, the foreign nationals were arrested for wilful trespass on state land or offences under the Women's Charter. If found guilty, they can be fined up to $1,000.
The commander of Ang Mo Kio Police Division, Assistant Commissioner of Police Keok Tong San, said: "We will not tolerate any form of criminal activity. Persons who think they can get away with their illicit activities by operating under the cover of forested areas are sadly mistaken. The Police will come down hard on such activities and weed them out wherever they may be."