In a recent letter sent to the State Securities Commission of Vietnam, Derrick Wan, representative of Singaporean Ministry of Finance, said the transaction was carried out mid March, according to Dau Tu Chung Khoan, a news website run by the Ministry of Planning and Investment.
The news report on March 21 did not say which entity represented the Singaporean government's stake.
Last week local media reported that Singaporean sovereign fund GIC was one of the foreign investors buying 45 million shares of Masan from Singaporean private fund Orchid Capital Investments.
The shares, reportedly sold for around VND1.3 trillion (US$57.65 million), were equivalent to nearly a stake of 6%.
Orchid Capital was the second foreign investor to divest from Masan since the beginning of this year.
Early this month the Hong Kong subsidiary of Switzerland-based financial group Credit Suisse sold its 8.9 million shares to two Vietnamese individual investors for VND660 billion (US$29.27 million).
Shares of Masan opened at VND70,000 (US$3.08) on March 22, unchanged from the closing on March 21 and down more than 2% from March 18.
Masan is a well-known food producer with a wide range of products including sauces, instant noodles and coffee.