A key economic adviser to Japanese Prime Minister Shinzo Abe said boosting fiscal and monetary stimulus at the same time would be a good strategy, while playing down the likelihood of employing so-called helicopter money.

Japan needs to keep various policy options open, including coordinated action by the government and central bank, Koichi Hamada said in an interview Wednesday.

Helicopter money, an unorthodox policy approach in which the Bank of Japan could directly fund government spending, would be a "very risky gamble," said Hamada, 80, noting that history has shown the dangers of unstoppable inflation.