BEIJING (AP) — China held sea and air combat drills Wednesday at disputed Scarborough Shoal, an uninhabited area of reefs and rocks it had seized from the Philippines in the South China Sea.

China on Sunday published new baselines for the shoal including geographic coordinates. A nation’s territorial waters and exclusive economic zone are typically defined as the distance from the baselines.

Tensions between China and the Philippines have been building over their competing claims to Scarborough Shoal and other outcrops in the South China Sea. Clashes have occurred including the Chinese coast guard firing water cannons at Filipino ships.

“This is a patrol and guard activity carried out by the theater troops in accordance with the law," the People's Liberation Army's southern command said in a short statement.

China seized the shoal, which lies west of the main Philippine island of Luzon, in 2012, and has since restricted access to Filipino fishermen there. A 2016 ruling by an international arbitration court found that most Chinese claims in the South China Sea were invalid but Beijing refuses to abide by it.

The Philippine Department of Foreign Affairs summoned the Chinese ambassador in Manila to protest China's baselines around Scarborough Shoal.

The department said the baselines infringe upon Philippine sovereignty and contravene international law, particularly the 1982 U.N. Convention on the Law of the Sea and the 2016 arbitration. The baselines have no legal basis and are not binding on the Philippines, it said.

Philippine President Ferdinand Marcos Jr. signed two laws last week reaffirming the extent of his country’s maritime territories and right to resources, including in the South China Sea, in a move that angered China.

China's claims to almost the entire sea overlap with claims by the Philippines, Vietnam, Indonesia and other governments.