Describing the reference as "inappropriate," Sakai said that Tokyo had sent a relevant reminder to the US.
"It is our country's position that the Sea of Japan is the single internationally-established name", the official added, as quoted by the news agency.
Earlier in the day, Capt. Mike Kafka, US Indo-Pacific Command public affairs officer, used the term "East Sea" when referring to Pyongyang's morning launches.
Japan and the two Koreas have long been at odds over the name for the waters they border. While Tokyo insists on the "Sea of Japan" term, Seoul and Pyongyang push for the "East Sea" and "Korean East Sea," respectively.
