The Philippine president says his militarily inferior country can't stop China's actions in contested waters, responding to a reported plan by Beijing to construct an environmental monitoring station in a disputed shoal off the Philippines' northwest coast.

President Rodrigo Duterte, however, warned Sunday that he would invoke a July 12 arbitration ruling that invalidated China's territorial claims in the South China Sea if the Chinese "start to tinker with the entitlement," apparently meaning when Beijing starts to tap the offshore area's resources.

Duterte's remarks differ slightly from those of Manila's Department of Foreign Affairs, which said that it was trying to verify the news reports about China's construction plans on Scarborough Shoal and that it would refrain from commenting while doing so.