Photo/Illutration A signboard of Nippon Steel Corp. (Asahi Shimbun file photo)

Nippon Steel Corp. has filed a patent infringement lawsuit against trading house Mitsui & Co. at the Tokyo District Court, the Nikkei business daily said on Thursday.

In October, Nippon Steel filed lawsuits against Toyota Motor Corp. and China's Baoshan Iron & Steel Co., alleging the two firms have infringed on its patents on non-oriented magnetic steel sheets that are used in electric vehicles.

Nippon Steel suspects Mitsui was involved in the matter, the Nikkei said. Neither company were immediately available for comment.

Toyota said in a statement to Reuters in October that the Nippon suit was "very regrettable" and that it had found no patent infringement issues. Baosteel said it did not agree with Nippon's claims and it would "firmly" defend its rights and interests.