Indonesian President Joko Widodo boarded a warship patrolling waters off the Natuna Islands on Thursday to assert sovereignty amid a row with China over fishing rights in the area.
China lodged a strong protest with Indonesia last week after Indonesian warships fired shots at Chinese fishing boats accused of stealing fish in what Jakarta says is part of its exclusive economic zone.
China's Foreign Ministry said the incident occurred on what it described as "traditional fishing ground where China and Indonesia have overlapping maritime rights claims."
The Natuna Islands and surrounding waters are the closest to the Nine-Dash Line, a demarcation used by China as the basis of its unilateral claim to a majority of the resource-rich South China Sea.
Vietnam, Taiwan, the Philippines, Malaysia and Brunei claim parts of the sea, but Indonesia has denied an overlapping claim with China.
"We discussed the economic and sovereignty aspects," Security Minister Luhut Binsar Pandjaitan said after a meeting on the Imam Bonjol warship attended by senior cabinet members.
"We don't want anything that disturbs stability in this area," he said in a statement.
Earlier Pandjaitan told The Jakarta Post that Joko's visit to Natuna will send a clear message that Indonesia is "very serious in its attempt to protect its sovereignty."
"In our course of history, we've never been this stern [to China]," Pandjaitan was quoted as saying. "This is to demonstrate that the president is not taking the issue lightly."
Pandjaitan added "we have already conveyed our position to Beijing, but we want to amplify it again in Natuna: We refuse to acknowledge the Nine-Dash Line and the claims of traditional fishing grounds."
Several Chinese military deployments to the region have been reported in recent months, while the US has sent naval ships to conduct freedom of navigation operations through the Spratlys, where China has reclaimed land for island-building.
Washington takes no official position over the competing claims, but says the issue should be resolved diplomatically and asserts the US right to freedom of the seas.