U.S. agricultural official J.B. Penn tried Tuesday to minimize the impact of a recent shipment of banned U.S. beef material, saying it was "an isolated incident" carried out by a meatpacker inexperienced in export procedures.

"We believe this was a case of a company and an inspector being only marginally involved in international commerce," the undersecretary for farm and agricultural services told a news conference at the U.S. Embassy after meeting with Japanese officials.

Penn said the firm's inspectors were not fully aware of the export requirements, leading to the shipment with vertebral column, which was supposed to be removed for the Japanese market.