Broadening price rises in Japan prompted some central bank policymakers to warn last month that inflation may overshoot expectations, highlighting the challenge Bank of Japan Gov. Haruhiko Kuroda faces in justifying ultralow interest rates.

One board member went as far as saying the BOJ must eventually communicate an exit strategy from ultraeasy policy, a summary of opinions at the September meeting showed.

While many opinions called for the need to keep monetary policy ultraloose to support the fragile economy, the comments highlight a gradual shift in the balance of the BOJ board, which was once dominated by proponents of aggressive easing.