TOKYO–Bank of Japan Gov. Haruhiko Kuroda on Friday voiced concerns about the rapid weakening of the yen after the currency hit its weakest level since 1998 against the U.S. dollar earlier this week.

“Rapid moves in foreign-exchange rates as seen in the past few weeks are not desirable because it would bring big uncertainty to companies’ business planning. That is negative for the economy,” Mr. Kuroda said at a press conference.

The comment signals a stronger warning from Mr. Kuroda, who previously said a weak yen USDJPY, +1.71% could be positive for the Japanese economy on the whole by boosting corporate profits earned overseas.

Earlier in the day, the bank’s policy board decided to maintain ultralow interest rates, moving against a global trend of monetary tightening amid inflation.

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The Japanese economy is still on the way to recover from the pandemic, and it isn’t appropriate to raise interest rates now, Mr. Kuroda said.

Write to Megumi Fujikawa at megumi.fujikawa@wsj.com