HANOI, May 16 (Xinhua) -- Vietnam's central bank on Wednesday adjusted up its reference exchange rate between Vietnamese dong and U.S. dollar by 20 Vietnamese dong to 22,568 Vietnamese dong per U.S. dollar.

With the current trade band of plus or minus 3 percent, the ceiling exchange rate is 23,245 Vietnamese dong per U.S. dollar, and the floor rate is 21,891 Vietnamese dong per U.S. dollar, said the State Bank of Vietnam.

Meanwhile, listed rates at big commercial banks in Vietnam remained unchanged from last week. Vietcombank and BIDV maintained both rates, buying the greenback at 22,735 Vietnamese dong per U.S. dollar and selling at 22,805 Vietnamese dong per U.S. dollar.

Last week, the reference exchanged rates saw four ups and one down with total magnitude of 26 Vietnamese dong and 18 Vietnamese dong, respectively.

According to Vietnam's National Financial Supervisory Commission, the central exchange rate in late 2017 rose around 1.6 percent against early 2017, while the average rate offered by commercial banks decreased 0.2 percent, and on the free market dropped some 1.5 percent.