HANOI, Dec 17 (Reuters) - Vietnam’s central bank said on Thursday it will work with U.S. authorities to ensure a “harmonious and fair” trade relationship, a day after Washington called Vietnam and Switzerland currency manipulators. The State Bank of Vietnam said in a statement that the country’s trade surplus with the United States was the result of “peculiarities of the Vietnamese economy”. The central bank said Vietnam’s monetary policies were not aimed at creating unfair trade advantage. (Reporting by Khanh Vu Editing by Ed Davies)