JAKARTA: 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 said on Tuesday.
The vessel entered Indonesia's 200-mile 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.
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.
A weeks-long standoff occurred in December and January when a Chinese coastguard vessel and accompanying fishing boats entered the northern Natuna Sea, prompting Indonesia to send fighter jets and mobilise its own fishermen.
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% of the South China Sea includes waters off the Natuna islands. An international arbitration panel in 2016 invalidated that line.
Foreign ministry spokesman Teuku Faizasyah reiterated that Indonesia does not recognise the line and has no overlapping claims.
China's defense and foreign ministries did not immediately respond to Reuters' requests for comment.