South Korean news media say the country's officials are criticizing the U.S. government's decision to call the body of water between Japan and South Korea the Sea of Japan, instead of the East Sea, as preferred by Seoul.

Koreans are campaigning for the international usage of the name East Sea, or at least both names.

But a spokesman for the U.S. State Department, Mark Toner, told reporters Monday that Washington authorizes only the name Sea of Japan.

At a regular daily briefing in Washington, Toner explained that the United States uses names decided by the U.S. Board on Geographic Names, which in this case is the name preferred by Japan.

South Korea's Yonhap news agency says Seoul has filed a formal protest with the United States against the decision. South Korea argues that the name Sea of Japan was unfairly established during Japan's 35-year colonial rule of the Korean peninsula in the early 20th century.

South Korea and Japan are also involved in a dispute over Liancourt Rocks, a group of islets in the same sea, claimed by both countries.