TOKYO, Oct 12 (Reuters) - Most Japanese government bond yields were flat on Tuesday after a moderately solid outcome of an auction for 30-year notes and as investors stayed cautious over rising U.S. Treasury yields. The 10-year JGB yield was flat at 0.09%, while the 20-year JGB yield was unchanged at 0.47%. The auction received bids worth 2.9 times the amount sold, lower than a book-cove-ratio of three times at the previous auction. The outcome was seen as “moderately solid” but it did not drive investors to place active bids because they were cautious about rising U.S. yields, a market participant said. Two-year Treasury yields leapt to a more than 18-month high during Asian trade, while the 10-year yield has now climbed about 30 basis points in three weeks. U.S. bond markets were closed on Monday for a holiday. In Japan, the 30-year bond yield rose 0.5 basis point to 0.7%, while the 40-year yield was flat at 0.78%. The five-year bond yield was flat at minus 0.08%, while the two year bond yield was unchanged at minus 0.12%. Benchmark 10-year JGB futures rose 0.05 point to 151.25. Reporting by Tokyo markets team; Editing by Subhranshu Sahu Our Standards: The Thomson Reuters Trust Principles.