Japan intervened unilaterally in the currency market to weaken the yen after it scaled another record high against the dollar on Monday (31 October), finance minister Jun Azumi said.

The high yen has been worrying Japanese automakers for months as it makes exports from Japan uncompetitve and reduces profits remitted from overseas subsidiaries. Announcing fiscal second quarter and first half financial results today, Honda Motor said lower vehicle unit volume in both periods was sue in part to "negative effects of yen appreciation".

Japan sold the yen for the second time in less than three months after it hit another record high against the dollar, saying it intervened to counter speculative moves that were hurting the economy, Reuters reported.

Finance minister Jun Azumi said Tokyo stepped into the market on its own at 10:25am local time (1:25GMT; 21:25EST) and would continue to intervene until it was satisfied with the results.

Tokyo's latest foray into currency markets followed weeks of warnings that its patience with the yen's strength was wearing thin, and came just days before the Group of 20 leaders' (G20) summit in Cannes, France, the news agency said.

The summit will focus on Europe's efforts to contain its sovereign debt crisis and avoid a repeat of the financial shock that roiled markets after the Lehman Brothers collapse in 2008.

Reuters said the Japanese government is keen to win G20 understanding that a strong yen is one challenge too many for an economy grappling with a nuclear crisis, a $250bn (GBP156bn) rebuilding effort from a March earthquake and tsunami, and ballooning public debt.

Japan also argues that the yen is sought by investors worried by the euro zone debt crisis and stuttering US growth and the demand has nothing to do with the fragile health of the Japanese economy.

The dollar rose over 4% past JPY79, from around JPY75.65, after Tokyo began selling its currency. The dollar had touched a record low of JPY75.3 earlier on Monday.

"I have repeatedly said that we would take decisive steps against speculative moves in the market," Azumi told a news conference. "Unfortunately it (the market) has not reflected our economic fundamentals at all."

Azumi said that while Monday's intervention was a solo act he was in a continuous contact with his international counterparts.

"I have been frequently in contact (with other countries) ... I have always conveyed Japan's stance and interests at senior official levels," he said.

Several G20 nations, including South Korea and Indonesia, have been intervening regularly in currency markets, but Japan is under more scrutiny as an issuer of one of three global currencies and does not want to be deemed a currency manipulator.

Following a G20 finance leaders' meeting earlier this month Azumi said the group's statement highlighting adverse effects of excessive currency swings reflected Japan's concerns.

He would not comment on the size of the intervention, but one trader told Reuters the authorities were intervening "quite persistently".

"My sense is that they might not quit very easily," a trader said.

The dollar remained near JPY79.20 for over an hour after the intervention due to a large bid at that level, prompting traders to speculate that Japan might want to set a Swiss-style floor for the dollar/yen.

However, Japanese officials said at the time of the Swiss Central Bank intervention in September to set a floor for the euro that the Japanese economy was too big for such a tactic, and dealers said Tokyo was unlikely to peg the yen to any particular level in the longer run.

Even though the yen's exchange rate when measured against a trade-weighted basket of currencies and adjusted for inflation is not far from its 30-year average, its rate against the dollar is much stronger than those assumed by Japanese exporters in their earnings projections, the report noted.

That has led to a flurry of warnings from leading companies that they might have no choice but to move more production abroad to cope.

"The effect of intervention is likely to be temporary but the authorities probably had to make a show of strength," Takafumi Yamawaki, chief fixed income strategist at JPMorgan Securities in Tokyo, told the news agency.

"The dollar/yen exchange rate is politically significant so they had to make an impact on the pair in one form or another, although intervening won't have much effect on the real economy."

Since September 2010, Japan has now intervened three times on its own and once jointly with other G7 rich nations to weaken the yen. But the effects of past intervention have proved fleeting in the face of steady demand from nervous investors seeking highly liquid and relatively safe assets such as Japanese government bonds.