TOKYO, Jan 9 (Reuters) - Japanese government bond prices dipped on Tuesday, with yields on 20 to 40-year bonds hitting one-month highs, after the Bank of Japan reduced its buying in those maturities over 10 years.
The BOJ trimmed the amount it bought in Japanese government bonds of 10 to 25 years left to maturity and those of 25 to 40 years to maturity by 10 billion yen ($88.39 million) each from its previous operations.
Since it adopted the yield curve control policy in 2016, the BOJ has occasionally tweaked its bond operations, with officials saying any changes are meant to keep bond yields in line with its policy goal and not to telegraph hints on its future policy.
While Tuesday's move was in line with slow and subtle reduction in its bond buying - which many market players call 'stealth tapering' - the timing took some players by surprise.
"Given that those maturities have become expensive on the yield curve, a cut in buying could happen any moment," said Ryoko Tada, fixed income analyst at Nomura Securities.
" But on the other hand, the BOJ could have done so back in December (when their yields were lower), so in that sense it was a bit of surprise," she said.
The benchmark 10-year JGB yield rose 1.0 basis point to 0.065 percent, its highest level in more than two weeks while the 20-year yield went up 1.0 basis point to 0.585 percent, a one-month high.
The 30-year yield rose 1.5 basis point to one-month high of 0.830 percent.
The price of the 10-year JGB futures dipped 0.10 point to 150.62 by late afternoon trade.
The five-year yield rose 0.5 basis point to minus 0.095 percent. (Reporting by Tokyo Markets Team; Editing by Shri Navaratnam)