A Japanese patrol boat sent a warning Friday to a South Korean research vessel after the ship was spotted in Japan's exclusive economic zone off Takeshima Island in Shimane Prefecture, Coast Guard officials said.
The vessel, which was conducting a marine survey without permission, left Japanese waters after receiving the warning, according to the 8th Regional Coast Guard Headquarters based in Maizuru, Kyoto Prefecture.
Under an international agreement, a country must receive permission to enter another country's exclusive economic zone to conduct marine research at least six months in advance.
South Korea had not submitted a request to enter the EEZ, the Coast Guard said.