NEW YORK (Yonhap News) ― The two Koreas have informally teamed up against Japan in a war of diplomacy in the United Nations on the naming of the waters near them, sources said Wednesday.

The 10th United Nations Conference on the Standardization of Geographical Names open earlier this week at the U.N. headquarters here, setting the stage for experts from around the world to discuss key issues relating to the handling of place names.

International organizations formally call the waters between the Korean Peninsula and Japan the Sea of Japan. But South and North Korea insist its original name is the East Sea and that should be used at least concurrently.

South Korean delegates are trying to publicize a nonbinding practice of using both of the names in case of disputes between countries, according to a U.N. source.

“North Korea directly requested the dual use of the names,” the source said, requesting anonymity. “South and North Korea are taking a virtually cooperative approach.”

But Japan claims that the single name should be maintained.

The ongoing U.N. conference is not aimed at produce a conclusion on the sensitive issue but it is important in enhancing

the awareness and understanding of the international community.

During a meeting of the International Hydrographic Organization in April, the South Korean government made a strong pitch for the East Sea to be used in the official maps of the international community.

The IHO, however, decided not to revise its current “Sea of Japan” appellation this time. The next session will be held in 2017.

Meanwhile, the U.S. made clear its longstanding policy of using a single name for the waters between Korea and Japan.

The State Department said, “We understand that the Republic of Korea uses a different term.”

The U.S., a key ally of both South Korea and Japan, has encouraged the two sides to “work together to reach a mutually

agreeable way forward with the International Hydrographic Organization on this issue,” it added.