"This is my last warning about the risk that the government will begin to intervene with support purchases to prop up the yen," said the Japanese government's foreign exchange chief, Atsushi Mimura.
The statement was made after the yen fell to 160 yen to the dollar overnight on Thursday.
The Japanese government has held talks with the Trump administration on the issue, according to Mimura.
Previously, Japan's finance minister, Satsuki Katayama, also called for support purchases of the yen, which then slowed the currency's fall.
A sharp weakening of the yen could force the Bank of Japan to tighten its monetary policy by raising interest rates.
