TOKYO, Dec 24 (Reuters) - Yields on long-ended Japanese government bonds tracked U.S. Treasury yields higher on Friday, while Japan"s benchmark 10-year bond yields were flat after moderately successful Bank of Japan"s bond-buying operation. The 20-year JGB yield rose 0.5 basis point to 0.470% and the 30-year JGB yield rose 0.5 basis point to 0.680 The 40-year JGB yield rose one basis point to 0.730%. The benchmark 10-year yield gained overnight as stock markets rallied on optimism about the public health impact of the Omicron coronavirus variant. The 10-year JGB yield was flat at 0.060%. The two-year JGBs were not traded and the yield remained at minus 0.100%, while the five-year yield was flat at minus 0.090%. Benchmark 10-year JGB futures fell 0.04 point to 151.83, with a trading volume of 6,994 lots.