The Hokkaido Prefectural Government launched an investigation Thursday into the discovery of metal fragments in unsalted butter imported from Germany by Sapporo-based Yotsuba Inc.

The fragments were originally discovered in 20 confectionery items manufactured and sold by Chateraise Co. of Kofu, Yamanashi Prefecture. The company said a man in Ono, Hyogo Prefecture, cut his mouth on a piece of metal in one of its muffins.

It said it is recalling 840,000 confectionery items on store shelves in 33 prefectures.

The butter was manufactured in Germany on Feb. 21, imported by Yotsuba and distributed to Chateraise and other food manufacturers in Japan.

Yotsuba said part of the filtering equipment was damaged and the metal pieces were mixed into the butter during the manufacturing process at the German company.