The city-state's central bank, Monetary Authority of Singapore (MAS), said it and the Commercial Affairs Department (CAD) of the police are currently investigating the breaches.
The Business Times newspaper said personnel from the MAS and the CAD, which fights white-collar crime, entered the trading floors of at least four brokerages earlier this week and took in some people, believed to be stockbrokers, for questioning.
In a statement, the monetary authority said it and the commercial affairs department were "jointly investigating possible contraventions of the Securities and Futures Act."
No other details were disclosed.
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Singapore closely guards its reputation as a regional financial centre and imposes tough penalties on white-collar crimes.
The Singapore Exchange (SGX) would not comment on the probe but said in a statement that it regularly refers cases of insider trading and market manipulation to the monetary authority.
In the first quarter of this year, the exchange said it referred three cases of insider trading and six cases of market manipulation to the authority.
Last year, it referred 11 cases of insider trading and 13 cases of market manipulation, the exchange said.