BEIJING, July 4 (Xinhuanet) -- A U.S. beef company is expanding a recall to 5.3 million pounds of ground beef after Federal investigators linked it to an outbreak of E. coli illnesses that has sickened 40 people in Michigan and Ohio.

    The USDA's Food Safety and Inspection Service said in a statement Thursday that Nebraska Beef Ltd.'s products may have been produced "under insanitary conditions."

    On Wednesday, The Kroger Co. expanded its voluntary recall of some ground beef products to its stores in more than 20 states, saying the meat may be contaminated with E. coli.

    The nation's biggest traditional grocer also urged customers to check the ground beef in their refrigerators and freezers to determine whether it is covered by the recall.

    The warning was issued as federal investigators try to locate the source of a separate salmonella outbreak linked to tomatoes that has sickened nearly 900 people, raising more questions about America's food safety system.

    While insisting that tomatoes remain the leading suspect, investigators are looking at other produce but remain mum on exactly what vegetables are getting tracked.

    Kroger's recall stems from meat obtained from Nebraska Beef Ltd., that has been linked to illnesses reported in Michigan and Ohio between May 31 and June 8 caused by E. coli bacteria.

    (Agencies)