Japan's finance ministry said on Monday it had conducted a coordinated yen-buying operation with the US last Friday, a rare move aimed at stabilizing the Japanese currency after it plummeted to fresh four-decade lows against the dollar​.

In a statement, Japan's Finance Minister Satsuki Katayama said the joint action "countered excessive volatility and disorderly movements in the Japanese yen in recent months," adding that the ministry remained "attentive and in close communication" with the US Treasury.

US Treasury Secretary Scott Bessent also confirmed Friday's effort in a social media post on Sunday, echoing Katayama's statement to say both sides “will not hesitate to participate in further joint intervention."

The yen surged more than 1% to 155.20 per dollar after the announcement, its strongest since early May, and well off the 40-year low near 164 hit last month. 

The joint intervention was the first following 2011's coordinated action to weaken the yen following the earthquake in eastern Japan.

Wei Liang, a researcher at the Institute of International Technology and Economy under the State Council's Development Research Center, told CMG that the recent rise in long-term US Treasury bond yields reflected concerns over US fiscal sustainability. He said the US may also be concerned that Japan's efforts to stabilize the yen could lead to large-scale selling of dollar assets, putting further pressure on financial stability.

This gives the US a reason to coordinate with Japan on currency intervention, he noted.

Some analysts questioned whether the latest intervention measures can offset the structural factors weighing on the yen, including higher fuel costs driven by the Middle East conflict and the still-significant interest rate gap between Japan and the US.

"The announcement effect of joint intervention is much bigger than solo action by Japan," said Tsuyoshi Ueno, a senior economist at NLI Research Institute.

"But the fundamentals driving yen weakness haven't changed, so we likely won't see one-sided yen rises from this intervention," he added.

(With input from Reuters)