Japan urged the United States on Friday to conduct strict investigations into the Jan. 20 discovery of material at risk of mad cow disease in a U.S. beef shipment, Japanese officials said.

The request was made when Agriculture, Forestry and Fisheries Minister Shoichi Nakagawa held talks with his U.S. counterpart, Mike Johanns, when they attended an informal World Trade Organization ministerial meeting in Davos.

Johanns apologized and told Nakagawa the shipment constitutes a violation of rules between the two countries, the Japanese officials said, adding Johanns expressed intention to submit to Japan a full report after thorough investigations.