Currency intervention is likely to prove ineffective in overturning the underlying weakness of the yen against the dollar, even as Japan's first attempt in 24 years in the foreign exchange market to strengthen its currency took immediate effect.

The dollar briefly plummeted below ¥141 from a 24-year high near ¥146 Thursday after the government stepped into the market to stem the yen's slide. The action took the market somewhat by surprise, even though repeated warnings by Finance Minister Shunichi Suzuki against the yen's recent rapid decline to 24-year lows against the U.S. currency had left the market nervous, said Masahiro Yamaguchi, head of investment research at SMBC Trust Bank.

An immediate sharp rally of the dollar looks difficult amid fears of another market intervention by Japanese authorities, at least for now. Still the dollar remains on course to return to the ¥145 level and possibly rise to ¥147.66, a level unseen in more than 32 years, market analysts say.