Japan stationed ground troops Monday on a remote island near a group of East China Sea islets that are disputed with China and Taiwan.
The Defence Ministry will keep a unit of 160 troops on Yanaguni Island to monitor vessels and aircraft in the region.
The island, with a population of 1,490, voted in favour of hosting the troops in a nonbinding referendum in February 2015.
Yonaguni is located about 150 kilometres south of the Japanese-administered Senkaku Islands. The uninhabited Senkaku islets are also claimed by China and Taiwan, where they are known as Diaoyu and Tiaoyutai, respectively.
Japan has enhanced defences near its south-western islands. Chinese coast guard ships have been spotted more often in the region since Tokyo’s purchase of three of the disputed islets in September 2012.
Tokyo’s move set off protests in dozens of Chinese cities and a boycott of Japanese products.