Sembcorp Marine (SembMarine) was the most heavily traded counter with 104.6 million shares changed hands.
In its filing as at 3.18pm on April 6, the market regulator has asked Yoma Strategic to reveal any possible explanation for the trading. It has also asked the company to confirm its compliance with the Mainboard listing rules.
In its response just over two hours later, Yoma says it is not aware of what might have caused the trading and that it believes it is in compliance with the relevant rules.
Yoma, with its focus on Myanmar, has been hit after the military coup early last year.
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Yoma shares closed April 6 at 18 cents, up 8.38% for the day and up 39.23% year to date.