TOKYO, May 25 (Reuters) - Yields on most Japanese government bonds (JGBs) were unchanged as weak results of a liquidity auction by the finance ministry was offset by an overnight retreat in U.S. Treasury yields. The auction for debt with remaining maturity of five to 15.5 years received bids worth 4.28 times the amount available, lower than a bid-cover ratio of 4.79 times at the previous auction. U.S. Treasury long-dated yields fell to two-week lows on Monday after a few Federal Reserve officials affirmed their support to keep monetary policy accommodative for some time. *Yield on the 20-year JGB fell 0.5 basis point to 0.440%. *Yields on other maturies were unchanged, with the 10-year JGB yield ending at 0.075% and the 30-year JGB yield closing at 0.670%. *The five-year yield was flat at minus 0.100% and the 40-year JGB yield was unchanged at 0.725%. *Benchmark 10-year JGB futures rose 0.04 point to 151.5, with a trading volume of 14,917 lots. (Reporting by Tokyo markets team) Our Standards: The Thomson Reuters Trust Principles.