One year since Beijing was defeated before the Hague-based Permanent Court of Arbitration, Manila has yet to push for the enforcement of the ruling and, under President Rodrigo Duterte, set it aside in exchange for investments and financial aid.
But Duterte had said he would eventually raise the ruling to China later in his administration, a move that could "lead to war," said retired Gen. Victor Corpus, who headed the Philippine military's intelligence service.
"If we pursue this decision of the Hague, China is ready to go to war to defend what it perceives as its territorial integrity and sovereignty," Corpus told a forum.
Corpus echoed observations by military analysts that China was fortifying its positions in the disputed waters to prevent a possible naval blockade by the United States in the event of a military confrontation.
Such a move would compromise China's security and economy, he said.
"Those are the real reasons why China built those islands. It is not for oil or gas or fish. It is for survival," he said.
"In order to ensure its survival, China will fight for those islands."
China has built artificial islands in the South China Sea and equipped them with runways, missile systems, and communication facilities.
It also seized control of Scarborough Shoal following a standoff with the Philippine Navy over Chinese poachers caught in 2012.
Asked what the Philippines should do in the face of China's construction in the disputed islands, Corpus said: "They fortify whatever they have now. We fortify whatever we have. Status quo."
"But we cannot prevent them (and say) 'You don't build this or build' that because they will not agree and if you meddle with those things, you will have war," he said.
Corpus said the Philippines need not bring up the arbitral ruling if it could agree with China to set aside their respective sovereignty claims and focus on other areas of cooperation.
Last May, both sides began a bilateral consultation mechanism that would eventually tackle the maritime dispute.
"Even if we debate for a hundred or even a thousand years, we will never come to an agreement and eventually, we will go to war," Corpus said.
Duterte earlier claimed Chinese President Xi Jinping had threatened war if the Philippines drilled for oil in the disputed waters.