The waters of the South China Sea are getting stormier than ever as Beijing and Manila trade barbs over an elusive “gentlemen’s agreement” that China claims has kept the peace in a disputed area of the waterway for years.

Recriminations over the deal, which China and former Philippine President Rodrigo Duterte have said was a spoken arrangement reached between the two countries over Manila’s moves near the disputed Second Thomas Shoal, have pushed tensions dramatically higher in the South China Sea.

While China claims some 90% of the energy-rich waterway that is also home to crucial trade routes, Manila insists that the Second Thomas Shoal falls within its exclusive economic zone — which extends 200 nautical miles (370 kilometers) from its coast — and has vowed that “it will never abandon the area.”