The downgrading of ratings on Japan's long-term local and foreign currency credit by Standard & Poor's Corp. could hurt Japan's economy by raising long-term interest rates, the head of the government's Tax Commission said Friday.

"Confidence in Japan has been damaged due to the accumulation of long-term debts, and the downgrading would affect bond prices," Hiromitsu Ishi, chairman of the commission, said in a speech in Tokyo. "Long-term interest rates would rise, and the Japanese economy would suffer considerable damage."

The U.S. rating agency said Thursday it has lowered its long-term local and foreign currency credit ratings for Japan to AA-plus from AAA.