Japan will closely monitor exchange rate movements, Finance Minister Yoshihiko Noda said Thursday after the U.S. dollar fell below 80 yen for the first time since March 18.

Noda, however, said the latest currency movements were different from a sharp fall in the dollar against the yen on March 17 in the wake of the March 11 deadly earthquake and tsunami in Japan, suggesting Japan may not intervene in currency markets to stem the yen's rise.

"We will closely monitor market developments," Noda told reporters on the sidelines of an annual meeting in Hanoi of the Asian Development Bank.

On March 18, the Group of Seven industrialized nations conducted a joint market intervention for the first time in more than 10 years to curb the strength of the yen, citing excess volatility and disorderly movements in exchange rates.

Noda said the dollar's fall Thursday reflected the currency's recent weakness and thin trading in Tokyo for a national holiday.

Asked whether authorities will step into markets to curb the yen's rise, the minister said he "will not answer a hypothetical question."

Japan's exchange rate policy is controlled by the Finance Ministry, with the Bank of Japan acting as its agent.