Japan's authorities declined to confirm overnight yen intervention after the currency surged 3.3% against the dollar in New York trading Thursday, its biggest intraday gain since December 2023. Finance Minister Satsuki Katayama said officials would "remain on high alert and respond as appropriate," while top currency official Atsushi Mimura hinted at support from US counterparts beyond "simply moral support."

A market participant said Japan intervened and US authorities conducted a rate check around 2:30am Tokyo time. The move came hours before the BOJ was expected to keep rates unchanged. South Korea also sold dollars, with the won strengthening to 1,417.10 versus the dollar. US Treasury Secretary Scott Bessent called the yen "very undervalued" and said "excess volatility" is unhealthy.

This would be the first intervention since April's Golden Week, when authorities spent a record ¥11.73 trillion over several days. Unlike April's clear warnings, Mimura kept a lower profile recently, suggesting authorities may have wanted to retain surprise. The Finance Ministry will release quarterly intervention data next week detailing April-June operations.