SHIMANE—A Japanese academic has discovered a map published in the United States in 1897 that marks Takeshima, a group of islets claimed by both Japan and South Korea, as Japanese territory.

Rikinobu Funasugi, an associate professor of history and geography at Shimane University, revealed the map as evidence the islets, called Dokdo in South Korea, were internationally recognized as Japan’s territory even before the Japanese government officially incorporated the islands into Shimane Prefecture in 1905.

The map was produced by an encyclopedia publisher based in New York. It was in the possession of an individual from Okinoshima, a town with jurisdiction over the islands.

The islands have been a source of a longstanding territorial dispute between Japan and South Korea.

The map in question shows Japanese territory in yellow and Korean territory in pink.

The Takeshima islands were presented in a yellow hue, accompanied by their British and French names--the Hornet islands and Liancourt Rocks, respectively.

The British and French names were also listed in the index under Japanese territory.

Funasugi said the recent discovery of the U.S. map showing the islands as Japan’s follows others made by Britain, France and Germany--all of which describe the islets as Japanese territory.