Reuters reports that Bank of Japan (BOJ) board member Hitoshi Suzuki said the central bank should allow super-long bond yields to rise moderately as part of efforts to make its stimulus programme sustainable.

"Allowing the super-long end of the yield curve to steepen moderately, while keeping 10-year bond yields around zero, would help financial institutions earn more profits," Suzuki told.

"As such, this will be desirable from the standpoint of maintaining financial system stability, as our monetary easing is prolonged," he said.

Suzuki also said the BOJ must seek to make its policy framework "sustainable and flexible", including its purchases of risky assets such as exchange-traded funds.

His remarks underscore a growing concern among policymakers over the rising costs of the BOJ's monetary easing, which has failed to fire up inflation to its elusive 2% inflation target.