The Philippine Coast Guard said on Saturday it had deployed a ship to Sabina Shoal on the Spratly archipelago, where it accused China of building an artificial island, having documented what it said were piles of dead and crushed coral on the sandbars.
Jonathan Malaya, spokesperson of the National Security Council (NSC), said NSC chief Eduardo Ano had ordered a tighter guard at locations within Manila's 200-nautical mile economic zone, as a long-standing diplomatic row with Beijing intensifies.
"No one will guard (these locations) except us. It is our responsibility under international law to guard (them) and ensure that the environment there would not be damaged and that there won't be reclamation activities," Malaya told a regular television program.
China claims almost all the South China Sea, including parts claimed by the Philippines, Brunei, Malaysia, Taiwan and Vietnam, and has carried out extensive land reclamation on some islands, building military facilities, causing concern in Washington and the region.
China's foreign ministry on Monday dismissed Manila's latest accusation as "groundless and pure rumour".
"Recently, the Philippine side has repeatedly spread rumours, deliberately smeared China and attempted to mislead the international community, which is futile," spokesperson Wang Wenbin told a regular briefing.
He urged Manila to "return to the right track of properly settling maritime disputes through negotiation and consultation".
Philippine Coast Guard spokesperson Jay Tarriela said its presence at the Escoda - or Sabina - Shoal had deterred China from doing small-scale reclamation, but that scientists would have to determine whether the piles of coral were natural or man-made.
He said the coast guard was committed to maintaining a presence at the shoal, just over 120 nautical miles from the Philippine province of Palawan.
The Permanent Court of Arbitration ruled in 2016 that Beijing's claims in the South China Sea, a vital waterway, had no basis under international law, a decision that China rejects.
The Sabina Shoal is the rendezvous point for vessels resupplying Philippine troops stationed on a grounded warship at the Second Thomas Shoal, where Manila and Beijing have had frequent run-ins.
Ano has called for Chinese diplomats to be expelled over the alleged leak of a phone conversation with a Filipino admiral about the maritime dispute.
On Monday, the Philippine foreign ministry said it would look into reports of "illegal and unlawful activities" by diplomatic officials, but did not name China.
