Preceding the announcement, President Donald Trump said on Sunday the United States was helping Japan to prop up the yen as a sign of friendship and to help the world economy.
"They have a weakening yen, and they wanted a little bit of help. And we're always there for Japan," Trump said aboard Air Force One.
The dollar fell 0.2 per cent to 157.07 yen after Trump's remarks, well off the 40-year high near 164 hit late last month.
Japan's Ministry of Finance said it conducted joint yen-buying intervention with the US Treasury Department on Friday.
The move "countered excessive volatility and disorderly movements in the Japanese yen in recent months", it said in a statement.
"The Japanese Ministry of Finance remains attentive and in close communication with our counterparts at the US Treasury. We will not hesitate to conduct further joint intervention," it said.
The joint intervention is the first since 2011, when the two countries took co-ordinated action to weaken the yen in the aftermath of the earthquake in eastern Japan.
Japan has been struggling to curb a relentless drop in the yen that pushes up import prices and stokes broader inflation, hitting households' wallets and Prime Minister Sanae Takaichi's public approval ratings.
Japan may have sold as much as $US58.97 billion to buy yen when it intervened in New York markets on Thursday, Bank of Japan data indicated, followed by another suspected foray into
On Friday, the US Treasury told a number of banks it too might intervene in the yen market, a source told Reuters, while Treasury Secretary Scott Bessent - who had said the yen "seems very undervalued" — had a handwritten "To Do" list at a cabinet meeting that said, "Buy Japanese Yen (JPY) $5-10 bil", a Reuters photo showed.
In line with Bessent's repeated calls for higher Japanese interest rates, the Bank of Japan on Friday offered its most explicit signal to date of an early rate hike, even as it kept monetary policy steady.
In a sign of broader policy co-ordination, South Korea stepped in to buy its won currency on Thursday.
Japan intervened in April and May, buying yen, causing only a brief rebound. The BOJ's June rate hike to a 31-year high of 1 per cent also gave the struggling currency little lasting boost.
