Reuters reports that the Bank of Japan is heading in the right direction in "stealth- tapering" its huge asset purchases given the damaging side-effects of prolonged monetary easing, said opposition heavyweight Banri Kaieda.

"Negative rates helped stem unwelcome yen rises, which is an accomplishment that must be recognised," Kaieda told Reuters in an interview on Monday.

"We now need to fix the side-effects, though this will take time," he said, pointing to the pain that years of ultra-low rates is inflicting on financial institutions' profits.

The comments highlight changing public sentiment over the role of monetary policy, as years of heavy money printing have failed to fire up inflation towards the central bank's 2% target and forced it to maintain its radical stimulus longer than expected.

Kaieda said the BOJ made the right move by fine-tuning its policy framework in March, allowing bond yields to move more flexibly and ditching a numerical target for the pace of its purchases of exchange-traded funds (ETF).

"The BOJ is already stealth-tapering," Kaieda said, adding that it was an "absolutely right decision" to start with its ETF purchases in heading toward an exit from ultra-loose policy.