The Indonesian navy has stepped up surveillance around the Natuna islands in the South China Sea after Chinese and American ships were found near overseas waters. However, they said the ships were undisturbed, a naval official said.
On Thursday, five naval vessels, aided by air traffic controllers, have been deployed to the North Natuna Sea to protect the area, Western Indonesian military commander Arsyad Abdullah told reporters.
"The North Natuna Navy is powerful in defending national interests within the Indonesian mandate in accordance with national law and international law which has been ratified so as not to tolerate any violations in the North Natuna Sea," Arsyad said.
In 2017, Indonesia renamed the northern regions of its exclusive economic zone in the South China Sea as the North Natuna Sea as part of a retreat against China's maritime ambitions.
Arsyad said American and Chinese warships had been found recently but said they were not a nuisance, adding that they were in foreign waters.
The weeks-long halt in Natuna took place in early January last year when a Chinese coastal ship and its accompanying fishing boats entered the northern Natuna Sea, prompting Indonesia to send fighter jets and reunite with its fishermen.
"There is no dialogue when it comes to our sovereignty, the territory of our country," said Indonesian President Joko Widodo following the incident.
In 2016, an Indonesian naval ship also shot at a Chinese fishing boat accused of illegal fishing near Natuna, following a series of conflicts that year.
That same year Indonesia also deported 23 foreign fishing boats from Malaysia and Vietnam accused of illegal fishing in Indonesian waters.
Marine and Fisheries Minister Susi Pudjiastuti said his company had sunk 10 Malaysian and 13 Vietnamese boats caught fishing illegally in Indonesian waters.
China has not yet claimed the islands of Natuna but says it has close fishing rights within the so-called "nine-line line" that encompasses most of China's wealthiest seas.
The claim is being rejected by other countries in Southeast Asia and is still universally accepted by the Permanent Court of Arbitration in The Hague.