The discovery was made in the port city of Busan in a shipment from the Cargill company, the Yonhap news agency said.

Since January 2006, South Korea has only allowed boneless beef from cows under the age of 30 months into the country as a preventive measure against spreading bovine spongiform encephalopathy, or mad cow disease.

Cargill has five plants in South Korea, and four of them have had their processing permits revoked following earlier discoveries of ribs and backbones in shipments, the report said.

Tuesday, Seoul revoked the license of a meat processing plant run by Swift & Co. from exporting to South Korea after a box of ribs was found by inspectors.