Oct. 8 (UPI) -- A Chinese oceanographic research ship conducted activities in Japan's Exclusive Economic Zone without prior notice, according to a Japanese press report.
NHK reported Monday the ship was active near Hateruma Island, Okinawa Prefecture, and the vessel entered Japan-clamed waters around 4:20 p.m. Sunday.
The ship was in an area about 120 miles southeast of Hateruma. The vessel was identified as the Xiangyanghong, No. 10, and was seen lowering a steel rope into the ocean, according to Japan's maritime security.
The activity was observed from a Japanese surveillance plane.
The Japanese coast guard said the Chinese vessel was conducting some kind of investigation. Conducting activities within Japan's EEZ without receiving prior permission is inadmissible, the coast guard said.
The Chinese government did not issue a response.
Japan and China have disputed claims in the East China Sea, including over the Japan-administered Senkaku Islands.
In alliance with the United States, Australia and India, Tokyo's maritime self-defense force has stepped up joint drills with partners in the Indian Ocean, possibly to send a warning to China.
Jiji Press reported last week Tokyo conducted joint exercises with the Sri Lankan navy for several days.
The drill was held near a crucial sea route for crude oil transportation from the Middle East.
Officers of the Sri Lankan navy boarded the Japanese destroyer, Kaga, where the two sides shared information on rescue operations and humanitarian assistance, according to the report.
"It's rare for the [maritime self-defense force] to allow military officials of other countries to board any of its vessels during an exercise at sea," a public relations official of the Defense Ministry's Maritime Staff Office said.