The new interbank rate has been increased by VND15 to VND20,723 a dollar, after rising by VND20 a dollar last weekend.
Most banks began to trade the greenback at VND20,895 to VND20,930.
On the unofficial market, the selling rate remained stable at VND21,370-21,470.
The interbank exchange rate has risen by 0.46 per cent since September 7, when the central bank said the depreciation this year would not be more than 1 per cent.
Thoi Bao Ngan Hang (Banking Times) newspaper said the central bank sold $150 million in the market in the first week of this month to stabilise the exchange rate.
Reuters said $1.5 billion had been used in three weeks since mid-August to import gold.
Newswire DVT.vn reported that the central bank had pumped in a total of $1.8 billion in the last two months to stabilise the exchange rate.
The Banking Times said the dollar deposit in banks in Ho Chi Minh City was estimated at $6-7 billion, which was adequate to stabilise the rate.
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