With the yen nearing a post-World War Two high, Japan has intervened to weaken the currency.
The government and central bank hope to safeguard the country’s economic recovery following the earthquake and tsunami in March.
It follows official warnings that the yen, largely driven by dollar weakness, had passed levels that the export-reliant economy could live with.
Finance Minister Yoshihiko Noda declined to comment on the size of the intervention on the currency markets or whether Tokyo will continue to intervene.
While an intervention in March was backed by leading economic powers, this time Japan acted unilaterally. Its move pushed the yen down to about 78.3 to the dollar from a level of around 77.