The yen has hit its highest level in three months after Washington and Tokyo launched a combined operation to support the Japanese currency.The yen strengthened to ¥155 to the US dollar on Monday, its highest level since early May, as the two governments confirmed they had carried out a rare joint currency intervention late last week.Tokyo’s finance ministry said on Monday that Japan and the US had conducted coordinated yen-buying intervention and will not hesitate to take further action.The joint action came after the yen weakened to a 40-year low of almost ¥164 to the dollar last week, and pushed the Japanese currency up by almost 4% last week.Donald Trump told reporters on Sunday: “They have a weakening yen, and they wanted a little bit of help. And we’re always there for Japan.”The yen had weakened in recent months as Japanese borrowing costs remained lower than in other advanced economies. This disparity fuelled a “carry trade”, in which investors borrowed cheaply in yen to buy higher-yielding dollar assets.The yen has also suffered from investors’ concern about Japanese prime minister Sanae Takaichi’s push for fiscal stimulus measures, and her criticism of higher interest rates, which have also pushed up Japan’s borrowing costs.skip past newsletter promotionafter newsletter promotionThe US Treasury secretary, Scott Bessent, said Washington “will not hesitate to ⁠participate in further joint intervention”, while repeating calls for further interest rate rises from Japan’s central ​bank. On Saturday, a photograph of Bessent’s notebook taken during a cabinet meeting showed that his “to do” list included buying $5bn-$10bn ⁠worth of Japanese yen.The consultancy Oxford Economics said the US-Japan coordinated intervention would not be enough to reverse the trend of yen weakness.“Despite rising market speculation about faster rate hikes by the Bank of Japan, we continue to assume the central bank waits until December because the intervention reduces the risk of a sharp yen depreciation and gives the BoJ more time to assess the impact of the Middle East conflict and past rate hikes on the economy,” it said.