Japan will respond "appropriately" to excessive volatility in foreign exchange markets, its top currency diplomat said Wednesday, after the U.S. dollar crossed the 144 yen line, an over seven-month high.

"We will closely watch developments in the currency market with a sense of increased urgency and respond appropriately if (forex) moves become excessive," Masato Kanda, vice finance minister for international affairs, told reporters.

The comment is the latest warning made by Japanese authorities, who are increasingly on alert against what they see as the yen's "rapid and one-sided" depreciation relative to the dollar.

The yen is weakening against the dollar and the euro, as the Bank of Japan's persistence in maintaining its monetary easing policy stands in stark contrast with the U.S. Federal Reserve and the European Central Bank, which have been raising interest rates to tamp down inflation.

Japanese authorities repeatedly issue verbal warnings before they intervene in the currency market. The last time Japan conducted a yen-buying, dollar-selling intervention to arrest the Japanese currency's decline was in October.