"China must be reminded that maritime and territorial claims are subject to established international legal procedures and dispute settlement mechanisms, not through unilateral proclamations or social media posts," Philippine foreign ministry spokesperson Rogelio Villanueva told a briefing.
Villanueva said the Philippines had "indivisible, incontrovertible and longstanding sovereignty" over Scarborough Shoal and the islands Manila holds in the Spratly archipelago.
The remarks are the latest in a war of words between Philippine officials and the Chinese embassy in Manila over disputes in the South China Sea.
China's embassy did not immediately respond to a request for comment.
The Philippines and China both lay claim to the Scarborough Shoal, which is effectively under Beijing's control through continuous deployment of its coast guard. Sovereignty over the atoll has never been formally established.
Villanueva was responding to a weekend social media post by the embassy that said a former Philippine ambassador had told a German radio station that Scarborough Shoal did not fall within Manila's territory.
Located 200km off the Philippines and inside its exclusive economic zone, the strategic shoal is located close to major shipping lanes and is coveted for its fish stocks and a turquoise lagoon that provides safe haven for vessels during storms.
"Sovereignty is not merely claimed, it is exercised," Villanueva said.
The Philippines and China have been locked in a series of maritime confrontations in recent years, with the Philippines accusing Beijing of aggressive actions inside its EEZ.
Those include water-cannoning and interference in resupply missions to Philippine-held features that Manila has often called "dangerous manoeuvres". China has insisted its coast guard has acted professionally to defend what is its territory.
The Philippines won a landmark case at the Permanent Court of Arbitration in 2016 that found China's sweeping claim of sovereignty in the South China Sea had no basis under international law, a decision that Beijing continuously rejects.
