Indonesian coast guard personnel received training provided by their Japanese counterparts on ways to deal with suspicious ships. The instruction took place in the capital Jakarta.
Ten officials from the Indonesian side took part in the training session on Tuesday and learned techniques from Japan Coast Guard officials on subduing crew members.
Indonesia is the world's largest archipelago nation and shares a key sea lane through the Strait of Malacca and the Singapore Strait with other countries. About 90 percent of the crude oil that Japan imports comes through the straits.
Indonesia designates waters in the southern part of the South China Sea as its exclusive economic zone. The Southeast Asian nation is at odds with China, which claims almost all of that sea.
Indonesia's coast guard has just 10 patrol ships. The country is working to improve its maritime patrolling capabilities by stepping up cooperation with other nations including the United States, which is providing Indonesia with financial support.
An Indonesian coast guard official said there are many spots in the vast ocean where crimes can happen, and wants to be ready to deal with any incident.
Ishizuka Ikuko from the Japan Coast Guard said she hopes to deepen a relationship of trust between the two countries and wants to contribute to the realization of a free and open Indo-Pacific region based on the rule of law.