The yield on 30-year debt rose 1 basis point to 1.890 percent, while the 20-year yield added half a basis point to 1.670 percent.
Investors continued to focus on a speech by US Federal Reserve Chairman Ben Bernanke on Friday at an annual central bank event in Jackson Hole, Wyoming, for hints on the likelihood and timing of a third round of quantitative easing, or QE3. The Fed chief has used the event for the past two years to reveal the bank's policy intentions.
"Everyone is just taking a wait-and-see stance ahead of Jackson Hole, with no incentive to buy the long end now," said a fixed-income fund manager at a Japanese asset management firm.
Some market participants said that no matter what Bernanke says this week, US data could speak louder than his words in predicting the likelihood of stimulus steps. The key non-farm payrolls report is due a week after Bernanke's speech, ahead of the Federal Open Market Committee's next meeting on Sep. 12-13.
"Even more key than whatever Bernanke signals at Jackson Hole will be the employment figures on Sep. 7, which comes ahead of the FOMC's next meeting," said Ayako Sera, senior market economist at Sumitomo Mitsui Trust Bank.
The benchmark 10-year JGB futures contract rose 0.02 point to 143.84, edging away from a 2-1/2-month low of 143.27 hit o n Aug. 16. Futures continued to hold above technical support at their 14-day moving average at 143.72.
The 10-year yield was flat at 0.805 percent.