The U.S. Justice Department has demanded that Kobe Steel Ltd. provide information related to its faked product data scandal, the embattled steel maker said Tuesday.

Company sources meanwhile revealed that the shady practice may have started more than 10 years ago.

The company said last week that the oldest misconduct it has uncovered so far dates back to 2007. But the sources said irregularities over quality control at Kobe's plants in Japan could date back more than a decade as the scope of suspected products expands from aluminum and copper to steel, Kobe's mainstay product.