TOKYO, Aug 4 (Reuters) - Japanese government bond yields fell on Wednesday, with the 10-year yield touching a seven-and-a-half-month low of zero percent, underpinned by concerns over the Delta variant and strong results of the Bank of Japan’s bond buying operation. An auction of 2.6 trillion yen 10-year JGBs on Tuesday attracted decent demand even as the yield stood near its lowest levels so far this year, rendering a support for the market. “Yesterday’s auction confirmed there is reasonable demand even at the yield of 0.01%. But there is a wall before going into negative levels, and I think we need fresh catalysts for that to happen,” said Ataru Okumura, strategist at SMBC Nikko Securities. The 10-year JGB yield fell 0.5 basis point to 0.000%, touching zero percent for the first time since Dec. 16. On Tuesday there was no trade in the benchmark issue, the first time in about two months. At the longer end, the 20-year JGB yield fell 1 basis point to 0.370%, also a seven-and-a-half-month low, while the 30-year yield dropped 0.5 basis point to 0.625%. The five-year yield fell 0.5 basis point to minus 0.135%, a low last seen in September last year. The BOJ bought JGBs in three maturity-based categories, those with one to three years, three to five years and 10 to 25 years to maturity on Wednesday. Its buying in the three to five year zone produced particularly strong results, market players said. Benchmark 10-year JGB futures price rose 0.06 point to 152.50. Reporting by Japan Markets Team; Editing by Amy Caren Daniel Our Standards: The Thomson Reuters Trust Principles.