The yen jumped to an 18-month high against the dollar on Tuesday, extending gains on persistent doubts the Bank of Japan will intervene to stem a dramatic rise that has undermined attempts to reflate the world's third-biggest economy.
The yen has risen over 12 percent against the dollar so far this year, extending gains after the BOJ surprised investors last week by refraining from more stimulus.
A further rise would intensify speculation of BOJ intervention sooner rather than later, as Japanese politicians have raised concerns about the yen's run-up.
"The bar for intervention is so high. At this stage, the market is skeptical whether they will follow through," said Steven Englander, global head of G10 FX strategy at Citibank in New York.