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Traders said liquidity, already low due to the Bank of Japan's regular debt buying operations, has dried up further as many investors opted for the sidelines before the fiscal year-end.
A rally in U.S. Treasuries on Friday helped limit losses in JGBs.
June 10-year JGB futures eased 0.08 point to 147.36.
The benchmark 10-year JGB yield rose 1.5 basis points to 0.385 percent, but below 0.405 percent touched on Friday when investors sold to book profits before the end of the fiscal year.
The 20-year yield was up 1 basis point at 1.145 percent .
Treasuries gained on Friday, helped by mildly hawkish comments from Federal Reserve Chair Janet Yellen and investor demand stemming from month-end portfolio rebalancing.