Indonesia will increase maritime security operations near some of its islands in the South China Sea after a Chinese coastguard vessel was spotted nearby, raising suspicions about its intentions, a senior security official says.
The vessel entered Indonesia's 322km exclusive economic zone (EEZ) off the northern Natuna islands on Saturday and left on Monday after radio challenges over jurisdiction, Aan Kurnia, chief of the maritime security agency, Bakamla, told Reuters.
Under international law, innocent passage is permitted through another country's EEZ but Aan said the vessel was lingering too long.
"Because this one floated, then went circling, we became suspicious, we approached it and learned that it was a Chinese coastguard vessel," he said, adding the navy and coastguard would boost operations in the area.
Wang Wenbin, China's foreign ministry spokesman, said the ship was undertaking "normal patrol duties in waters under Chinese jurisdiction".
"China's rights and interests in the relevant waters in the South China Sea are clear," Wang told a news conference.
Indonesia renamed the northern reaches of its EEZ in 2017 as the North Natuna Sea, pushing back against China's maritime territorial ambitions.
While China has made no claim to the archipelago, the presence of its coastguard so far from the mainland has concerned Indonesia, aware of numerous encounters that Malaysia, the Philippines and Vietnam have had with Chinese vessels inside their EEZs, which have disrupted fishing and energy activities.
China's coastguard fleet includes converted navy frigates and often operates alongside fishing boats described by experts as state-backed militia. China says its coastguard operations are legitimate.
The "nine-dash line" that Beijing uses on maps denoting its claim to 90 per cent of the South China Sea includes waters off the Natuna islands. An international arbitration panel in 2016 invalidated that line.
Australian Associated Press