Japan has stepped up its warning to currency markets that it is prepared to respond to excessive yen weakness, with Tokyo and Washington delivering a coordinated message that officials hope will deter traders from pushing the currency lower.
Japan’s top currency diplomat Atsushi Mimura said Monday that markets should take the recent message from Japanese and US officials “at face value,” signaling that Tokyo remains prepared to act if yen depreciation becomes disorderly.
“Japan’s prime minister, finance minister and the US have sent a very clear message. Markets should take that message at face value,” Mimura said in an interview with Reuters. “I will be watching closely whether markets will continue to take (the message) at face value.”
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The comments came after US President Donald Trump raised concerns about yen weakness during a summit with Japanese Prime Minister Sanae Takaichi, according to Japanese Finance Minister Satsuki Katayama.
Katayama and US Treasury Secretary Scott Bessent subsequently reaffirmed in a phone call that the yen’s undervaluation was a concern, reinforcing the impression that Washington is comfortable with Tokyo’s efforts to prevent excessive currency weakness.
The yen strengthened sharply following Mimura’s remarks, breaking through the 157-per-dollar level to trade around 156.75.
The immediate market reaction emphasizes the importance of official communication when intervention risks are perceived to be rising. Tokyo does not need to announce an intervention to influence currency positioning. The prospect that authorities could intervene can itself raise the cost of betting aggressively against the yen.
Intervention Remains on The Table
Mimura stopped short of saying whether Japan was preparing another intervention. Asked whether Tokyo was ready to conduct another yen-buying operation, either independently or in coordination with the United States, he said: “I have nothing to comment on how we could act.”
That carefully worded response leaves the precise threshold for intervention unclear while preserving the government’s ability to respond if market conditions deteriorate.
Japan and the United States conducted a rare coordinated intervention on July 31 to prevent the yen’s decline toward a nearly four-decade low from destabilizing financial markets. Mimura previously described that operation as the culmination of the countries’ “currency alliance.”
He said the term was intended to describe cooperation extending beyond foreign exchange into economic security, critical minerals and global supply chains.
The significance of the latest US involvement is that Washington’s concerns over yen weakness could strengthen Tokyo’s ability to signal intervention without necessarily carrying it out.
Mimura also dismissed concerns that Japan could face financial constraints if it intervened again.
“I have absolutely no such concern,” he said.
Japan holds substantial foreign-exchange reserves that can be deployed in support of the yen, although the effectiveness and political consequences of intervention depend on market conditions and the broader monetary-policy environment.
Japan’s challenge is that intervention alone cannot easily eliminate the underlying monetary forces weighing on the currency.
The Bank of Japan has been raising interest rates, with its policy rate reaching 1.25% earlier this month. The increases are intended partly to address persistent inflationary pressure, including the higher import costs created by a weak yen.
Yet the yen has continued to face pressure because US interest rates remain considerably higher.
Mimura noted that the monetary-policy gap between the two economies has been narrowing as a trend, with the BOJ on a rate-hike path while the Federal Reserve has also been tightening.
“As such, the gap between Japanese and US policy rates has been narrowing as a trend,” Mimura said. “We are always mindful of such developments in watching market moves.”
The problem for Japan is that even a narrowing rate differential may not be enough to reverse yen weakness if markets expect US rates to remain elevated for longer. Higher US yields increase the attractiveness of dollar-denominated assets relative to Japanese assets, encouraging capital flows that can weaken the yen. That makes the currency particularly sensitive to changes in Federal Reserve expectations.
Weak Yen Adds to Japan’s Inflation Problem
The government’s concern is not simply the exchange rate itself. A weaker yen increases the cost of imported goods, including energy. That has become more significant as the Middle East conflict has pushed up fuel prices.
For Japan, which relies heavily on imported energy, simultaneous increases in global commodity prices and yen weakness can reinforce inflationary pressure. That has resulted in a difficult policy environment for the BOJ. Higher interest rates can support the yen by reducing the interest-rate differential with the United States, but tighter monetary policy can also weigh on domestic demand.
Meanwhile, intervention can smooth excessive currency movements but does not fundamentally change the interest-rate differential or the underlying demand for dollars. The authorities are therefore trying to influence market expectations while monetary policy does the longer-term work.
Mimura also pushed back against the argument that Japan’s fiscal policy is contributing significantly to the yen’s weakness. Some analysts have interpreted Bessent’s previous calls for Japan to “sit back and enjoy the success of Abenomics” as criticism of Prime Minister Takaichi’s spending plans.
Mimura rejected the idea that international partners have criticized Japan for running an excessively expansionary fiscal policy.
“I’ve never received any criticism from G7, G20 or other overseas counterparts that Japan’s fiscal policy is too expansionary,” he said.
The comments are relevant because currency markets are increasingly sensitive to the interaction between monetary and fiscal policy.
Large fiscal spending can support domestic demand and inflation, potentially putting upward pressure on interest rates. But if investors conclude that fiscal expansion will weaken confidence in Japan’s public finances, it can also weigh on the yen and government bonds.
For now, Japanese officials are emphasizing a different explanation: the yen’s weakness is being driven largely by international interest-rate differentials and market dynamics rather than an unsustainable domestic fiscal stance.
The Next Test Is Market Behavior
Mimura’s warning puts the yen market on notice, but the durability of the currency’s rebound will depend on whether traders believe Tokyo is genuinely prepared to intervene if necessary. The yen’s move to around 156.75 after his comments shows that official warnings can have an immediate impact. Sustaining that strength is more difficult.
If US yields remain elevated and the Federal Reserve maintains a hawkish stance, the fundamental incentive to hold dollars over yen could persist. Japan would then have to decide whether market movements have become sufficiently disorderly to justify direct intervention.
The stronger message from Washington gives Tokyo an additional layer of diplomatic support. But coordinated rhetoric is not a substitute for a sustained change in monetary-policy expectations.