PRESIDENT Rodrigo R. Duterte on Thursday said a 2016 United Nations (UN) arbitral ruling that favored the Philippines in its sea dispute with China is part of international law and should not be ignored.

“The 2016 arbitral award on the South China Sea is an authoritative interpretation of the application of UNCLOS,” he said in a speech at the 37th Association of Southeast Asian Nations (ASEAN) virtual summit hosted by Vietnam, referring to the UN Convention on the Law of the Sea.

“It is now part of international law. And its significance cannot be diminished nor ignored by any country, however big and powerful,” Mr. Duterte said, alluding to China’s refusal to honor the ruling.

Mr. Duterte echoed what he said in his most forceful defense of the arbitral award before the UN General Assembly in October —  his first since coming to power four years ago.

“The Philippine position is clear and firm. We must solve the disputes peacefully and in accordance with international law, including UNCLOS,” he said at Thursday’s ASEAN summit.

Mr. Duterte said the Philippines agrees with ASEAN in transforming the disputed waterway into a “sea of peace and prosperity for all.”

He also said the region has waited for a long time to come up with a substantive and effective Code of Conduct in the South China Sea.

The tough-talking Philippine leader also urged ASEAN to reject maneuverings by so-called external powers in getting countries in the region to choose camps. “This we must resist — consistently and firmly.”

Mr. Duterte said peace and stability could only be ensured by an open and inclusive order, where ASEAN remains the fulcrum of regional security processes and mechanisms.

“As we chart our community’s post-2025 future, it is crucial that we consolidate ASEAN’s position in the evolving regional order,” he said.

Mr. Duterte had sought closer trade and investment ties with China since he came to power in 2016, including potential joint explorations for oil and gas in the South China Sea.

The UN tribunal in 2016 ruled that China’s claim of historic rights to resources within the sea falling within the ‘nine-dash line’ was illegal. The court said the Philippines could declare certain areas of the sea as part of its exclusive economic zone because these areas do not overlap with any entitlements claimed by China.

Certain Chinese actions within the Philippines’ exclusive zone violated its sovereign rights and were unlawful, the court said. It added that China’s island-building activities in the disputed waterway had caused severe environmental harm in violation of international conventions.

In his speech, Mr. Duterte said the South China Sea dispute is ASEAN’s strategic challenge. “How we deal with this matter lays bare our strengths and weaknesses as a community. We must act with haste.”

In his speech before a virtual roster of world leaders that included US President Donald Trump and Chinese President Xi Jinping in October, Mr. Duterte said the arbitral award was “beyond compromise.”

He also said the Philippines rejects attempts to undermine the ruling that rejected China’s claim to more than 80% of the South China Sea, without naming China. His successor, Benigno SC. Aquino III, started the lawsuit. — Norman P. Aquino and Gillian M. Cortez