At 0130 GMT the dollar rose to 78.45 yen from 76.99 earlier. The last time Japan intervened was on March 18 with its G7 counterparts after the yen hit a post-war high of 76.25 to the dollar following a massive earthquake and tsunami.

Finance Minister Yoshihiko Noda confirmed that Japan intervened unilaterally in the foreign exchange market to counter what he called "one-sided" and "excessive" movements in the currency.

"If the moves continue, it could negatively impact the Japanese economy and financial stability when Japan is making various efforts to reconstruct itself from the impact of the disaster," Noda told reporters.

"Therefore we carried out currency intervention. Now we will watch market movements closely."

The Bank of Japan shortened its scheduled two-day meeting and was expected to decide on further monetary easing later on Thursday.

Copyright AFP (Agence France-Presse), 2011