Former Supreme Court Associate Justice Antonio Carpio on Thursday said Ayungin Shoal is part of the Philippines' exclusive economic zone (EEZ), stressing that Manila has the sovereign right to maintain and build structures there without China's permission.

Carpio made the statement in response to Chinese Ambassador Jing Quan's claim that the Philippines violated a supposed provisional agreement by allegedly conducting construction activities near the grounded BRP Sierra Madre.

The Chinese envoy earlier said Beijing dispatched two China Coast Guard vessels after observing Filipinos "building some kind of barrier nets" and carrying out what he described as construction work on the military outpost.

Carpio said the ambassador's statement "is worth interrogating."

"The Arbitral Award declared Ayungin Shoal part of the EEZ of the Philippines. In the EEZ there is freedom of navigation and overflight for all states. Any state can sail its vessels to Ayungin Shoal without seeking permission from any country," Carpio said.

"As the adjacent coastal state, the Philippines has the exclusive sovereign right to erect artificial structures on Ayungin Shoal without seeking permission from any state," he added.

The BRP Sierra Madre, deliberately grounded in Ayungin Shoal in 1999, serves as the Philippines' military outpost in the disputed area.

Armed Forces of the Philippines Chief Lt. Gen. Antonio Nafarrete likewise defended the actions of Filipino troops stationed aboard the vessel.

"That was ours, that was our military post," Nafarrete said in Filipino.

The latest confrontation prompted President Ferdinand Marcos Jr. to summon Chinese Ambassador Jing Quan to explain the incident.

Malacañang condemned the alleged assault by the China Coast Guard on Filipino troops assigned to the BRP Sierra Madre and backed the statements issued by the Department of Foreign Affairs, Department of National Defense, and the Armed Forces of the Philippines.

Carpio also urged the DFA to clarify the alleged provisional agreement cited by the Chinese ambassador, noting that the department has yet to publicly release the document.

"If that agreement prevents the Philippines from sending its vessels to Ayungin Shoal unless there is prior notice and consultation with China, or prevents the Philippines from erecting artificial structures on Ayungin Shoal, then such agreement is in derogation of the freedom of navigation and of the sovereign right of the Philippines under UNCLOS and the Arbitral Award," he said.

Carpio added that if the agreement indeed restricts the Philippines' activities in Ayungin Shoal, it would exceed the authority of the DFA secretary because it would diminish the country's sovereign rights recognized under the United Nations Convention on the Law of the Sea and the 2016 Arbitral Award.