Some Bank of Japan board members are concerned that increased bond purchases by the central bank may be viewed as financing government deficit spending, minutes of last month's meeting show. They said it was important "to clearly recognize and explain to the public" that bond purchases are not "for the purpose of monetization," the document on the BOJ website showed today. The planned purchase of about 40 trillion yen ($479 billion) of debt a year is a "large amount," they said.

Government fiscal burdens, such as Japan's public debt of twice the nation's gross domestic product, can increase pressure on central banks to sacrifice their independence and prop up state spending. In the absence of fiscal austerity measures, last month's expansion of bond buying could be seen as paving the way for monetization, JPMorgan Chase & Co. said previously in a report.

The BOJ is likely to "adjust the size of this asset- purchase programe very gradually and mildly" to avoid investors pricing in that risk, said Junko Nishioka, an economist at RBS Securities Japan Ltd. who has worked for the central bank.