MANILA- The Philippines has noted certain 'improvements' on structures that China put up on three of its artificial islands in the disputed South China Sea, Defense Secretary Delfin Lorenzana bared Tuesday.

Speaking before the the Management Association of the Philippines (MAP), Lorenzana said defense officials received information on the Chinese structures based on pictures taken in November and just last month.

He added that they have sought help from the United States, a top defense ally, to verify the data.

"We had to ask some of our friends, like the US," Lorenzana said as he gave a briefing on the Duterte administration's national security programs.

During the open forum, former Philippine Ambassador to the United States Jose Cuisia also asked Lorenzana if the Philippines has already filed a diplomatic protest in connection with the Chinese structures.

The Defense chief told Cuisia that officials have already communicated with the Department of Foreign Affairs for the possible filing of a diplomatic protest.

Lorenzana's report came amid a warming of ties between the Philippines and China despite the unresolved maritime dispute, with President Rodrigo Duterte pursuing friendlier ties with one of the world's largest economies.

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His statements also came as Foreign Affairs Secretary Alan Peter Cayetano held talks with visiting Chinese Foreign Minister Wang Yi. The two officials signed a memorandum of understanding to boost bilateral ties, a step that came two months since restarting direct negotiations on the sea dispute.

China has ignored the Philippines' July 2016 victory in its arbitration case, where a United Nations tribunal invalidated Beijing's nine-dash line claim.

It has instead stepped up militarization and island-building activities in the waters, threatening freedom of navigation in the vital sea lane.