Reiterating the country's "rules-based approach" to address the competing claims in the East Sea, Del Rosario said China and other parties to the dispute "cannot forever avoid" having their claims validated before the International Tribunal on the Law of the Sea (Itlos), or other UN mechanism.
"The community of nations must be governed by rules" and the Philippines is "resolved to hold sacrosanct the primacy of international law which levels the playing field between strong and weak countries," Del Rosario told an Ateneo de Manila University forum.
The reputedly oil- and gas-rich East Sea is claimed wholly or partially by Vietnam, Brunei, Malaysia, Taiwan, China and the Philippines.
Tensions in the decades-old dispute escalated this year amid accusations from the Philippines and Vietnam that China was becoming increasingly aggressive in staking its claims to the sea.
Del Rosario said the government is confronted with the enormous task of "protecting our territorial integrity in the western maritime frontiers of our nation."
"The promotion of national security, one of the three key pillars of Philippine foreign policy, rests first and foremost on establishing, defining and safeguarding our national territory, both terrestrial and maritime. Sovereignty and territory are fundamental requirements for the existence and continued survival of any nation-state," he said.
He told the forum that China's so-called "9-dash line" claim was the "crux of the problem."
China has asserted its territorial claim over the whole of the East Sea based on a map that shows a series of nine dashes or dotted lines forming a ring around the entire sea area, hence the "9-dash line."
If left unchallenged, "China's baseless claim over the entire East Sea would not only adversely affect our sovereign rights and jurisdiction, but it would also potentially threaten the freedom of navigation and unimpeded commerce of many other nations," he warned.
Del Rosario said that the Philippines is advocating two avenues in advancing its preventive diplomacy solution.
One is a proposal it has tabled in the Association of Southeast Asian Nations for a cooperative framework for managing disputes that will be vetted by Asean maritime legal experts scheduled to meet in September in Manila.
The second "involves having other parties join the Philippines in subjecting China's 9-dash line to validation, in accordance with Unclos."
Del Rosario said the Philippines has protested the "9-dash" map before the UN, along with Vietnam, Indonesia and Malaysia.
In Beijing, a strongly worded editorial in the China Daily on Friday accused the Philippines of infringing "China's territorial integrity" and said Manila could pay "a high price" for misjudging the issue.
The editorial came after a newspaper report that the Philippine Navy would soon complete a shelter to "protect troops guarding and securing the country's maritime domain" on an island claimed by both countries. The island is called Patag by the Philippines and Feixin by China.
"There could well be a high price to pay for any misjudgment on the East Sea issue by countries like the Philippines," the editorial said.