The yen has hit its highest level in three months after Japan and the US 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, after Tokyo and Washington confirmed they had carried out a rare joint currency intervention late last week.

Tokyo’s finance ministry said on Monday the two governments had conducted coordinated yen-buying intervention and would not hesitate to take further action.

The intervention came after the yen had weakened to a 40-year low of almost ¥164 to the dollar 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 so-called “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 to use tax and spending measures to stimulate the Japanese economy, and her criticism of the Bank of Japan setting higher interest rates, which have also pushed up the country’s borrowing costs.

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The 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.

This is the first collaboration involving Japan and the US since March 2011 when a joint intervention was made to weaken the yen after the March Tohoku earthquake and tsunami.

Lee Hardman, a currency analyst at MUFG bank, said: “The threat of further joint intervention and a faster pace of BoJ hikes should provide more support for the yen, and discourage speculators from running elevated short yen positions.”

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.