TOKYO, Sept 28 (Reuters) - Japanese government bond prices slipped on Monday after the Bank of Japan's bond buying operation showed strong selling interest ahead of a 10-year JGB auction later in the week.

The 10-year JGB futures price fell as much as 0.26 point to 148.08 following surprisingly weak results of the BOJ's 400 billion yen buying of bonds with five to 10 years to maturity.

The BOJ's buying attracted offers more than four times as large as the central bank's bids, highlighting strong selling pressure ahead of the 10-year bond auction on Thursday.

The yield on benchmark 10-year cash JGBs also rose 2.5 basis points to 0.345 percent, while the 20-year JGB yield rose 3.0 basis points to 1.125 percent.

(Reporting by Tokyo markets team; Reporting by Jacqueline Wong)