Some Bank of Japan policymakers believe the effects of the central bank's ultra-easy monetary policy might be "diminishing," referring to a temporary rise in long-term interest rates last month, minutes from its June policy meeting show.

Views on the matter were divided, however, during the June 18-19 meeting, with some members saying the effects "continued to be substantial," given low and stable interest rates "despite the rise in overseas interest rates," according to the minutes released Tuesday.

The meeting came a week after the country's key long-term interest rate hit a nine-month intraday high of 0.545 percent, echoing rises in European and U.S. equivalents. The yield on the benchmark 10-year Japanese government bond has since fallen below 0.5 percent.