China said Saturday a small civilian vessel from the Philippines had “illegally placed itself on the beach” of an atoll in the South China Sea that both countries claim.

The vessel, which landed on the Spratly Islands atoll on Friday, was there for supply purposes, the China coast guard posted on the Weixin platform.

The Philippines’ coast guard, national security council and foreign ministry did not immediately respond to a request for comment Saturday about the incident.

The Philippines has stationed a small number of troops on a World War II ship it grounded in 1999 as an outpost to reinforce its sovereignty claim over the Second Thomas Shoal, known as Ayungin in the Philippines and the Renai Reef in China.

Manila refused Beijing’s requests last year to tow the vessel away in the diplomatic row that has soured relations between the two Asian nations.

China asserts sovereignty over almost the entire South China Sea, including areas claimed by Vietnam, the Philippines, Malaysia, Brunei and Indonesia. The Permanent Court of Arbitration in 2016 ruled that China’s claims to economic rights across large swaths of the South China Sea had no legal basis.

Beijing fiercely rejected the decision by the Permanent Court of Arbitration.