The U.S. invasion of Iraq was a mistake based on a faulty assumption, Defense Minister Fumio Kyuma said Wednesday in a rare criticism from Washington's closest Asian ally.

Fumio Kyuma said he has expressed his understanding of the U.S. war in Iraq but never supported it, and "my opinion remains the same."

President George W. Bush's decision to invade Iraq "based on an assumption that weapons of mass destruction existed was a mistake," Kyuma told a news conference.