Japan intervened unilaterally in the currency market to weaken the yen after it scaled another record high against the dollar on Monday, Finance Minister Jun Azumi said.

Tokyo's foray into the market -- it's second in less than three months -- follows repeated warnings by policymakers that they were ready to act to prevent the yen's strength from hurting the world's third largest economy.

The dollar spiked more than 3 percent to as high as 78.55 against the yen from around 75.65 yen and a record low of 75.31 yen touched earlier on Monday.

Azumi told a news conference the solo intervention started at 10:25 local time (1:25 a.m. GMT). He declined to comment on the size of yen-selling, but added Tokyo would continue to intervene until it was satisfied with the results.

Azumi told reporters earlier that he was ready for firm measures and described the latest currency moves as speculative. He said there was no specific reason driving the yen to its latest record against the dollar.

I have said many times, if forex moves do not reflect the economic fundamentals and speculative moves last, Japan will take firm measures, Azumi told reporters.

Japanese corporate executives and policymakers have voiced increased alarm over the yen's steady climb past a succession of

records, largely driven by safe-haven flows fuelled by continued uncertainty about Europe's ability to contain its debt crisis.

(Additional reporting by Hideyuki Sano; Writing by Tomasz Janowski; Editing by Alex Richardson)