TOKYO (REUTERS) - Bank of Japan Governor Haruhiko Kuroda said the central bank has ample room to expand stimulus further and is prepared to cut interest rates deeper into negative territory, signalling a readiness to act again to hit his ambitious inflation target.

The BOJ unexpectedly cut a benchmark interest rate below zero on Friday (Jan 29), stunning investors with another bold move to stimulate the economy as volatile markets and slowing global growth threaten its efforts to overcome deflation.

But even after deploying what he described as "the most powerful monetary policy framework in the history of modern central banking", Mr Kuroda said he remained open to devising new means to revive the economy if existing tools did not work.

"If we judge that existing measures in the toolkit are not enough to achieve (our) goal, what we have to do is to devise new tools," Mr Kuroda said in a speech at a seminar on Wednesday (Feb 3). "I am convinced that there is not limit to measures for monetary easing," he said.

The central bank will charge a 0.1 per cent interest on some of the excess reserves financial institutions park with the BOJ, while maintaining its existing asset-buying programme - dubbed "quantitative and qualitative easing" (QQE).

Mr Kuroda countered criticism that the BOJ was running out of ammunition to accelerate inflation - which has ground to a halt due to slumping oil costs - to its 2 per cent target, saying negative rates will not hamper the bank's efforts to gobble up government bonds.

"If judged necessary, it is possible to further cut the interest rate from the current level of minus 0.1 per cent," he said.