JAKARTA, Indonesia, Oct 24, (AP): Indonesian patrol ships drove a Chinese coast guard vessel away from a survey vessel in a disputed area of the South China Sea for the second time in four days, Indonesian authorities said Thursday. Indonesia's Maritime Security Agency said the Chinese ship twice approached the MV Geo Coral, interrupting a seismic data survey being conducted by the state energy company PT Pertamina in a part of the South China Sea claimed by both countries.

China’s "nine-dash line,” which it uses to roughly demarcate its claim to most of the South China Sea, overlaps with a section of Indonesia’s exclusive economic zone that extends from the Natuna Islands. A 2016 international arbitration ruling involving the Philippines invalidated most of China’s sweeping claims in the sea, but China has ignored the ruling and called it a sham.

Chinese ships have regularly entered the area Indonesia calls the North Natuna Sea, fueling tensions between the countries. Indonesian authorities said the Chinese coast guard ship CCG 5402 was detected near MV Geo Coral on Monday. An Indonesian patrol ship contacted the ship, whose crew insisted that the area was under China's jurisdiction.

According to a statement issued Tuesday, Indonesian coast guard and navy ships then drove the Chinese ship away. On Thursday morning, the Chinese ship again approached the site of the seismic survey and did not respond to hails from the Indonesian coast guard, which again drove the vessel away, according to the Maritime Security Agency.

"Indonesia’s Maritime Security Agency will continue to conduct intensive patrols and monitoring in the waters of North Natuna to ensure that seismic survey activities run smoothly and maintain Indonesia’s sovereignty and sovereign rights,” said the statement. Clashes at sea between China and its maritime rivals have become increasingly common in recent years, driving tensions especially with the Philippines and Vietnam.