Hundreds of Chinese fishing vessels, which seem to be part of China's maritime militia, have been swarming the vicinity of Pag-asa Island and nearby islands in the West Philippine Sea. The military earlier said the foreign vessels might be monitoring rehabilitation efforts on Pag-asa Island.

National Security Adviser Hermogenes Esperon Jr. said declaring the concerned areas as marine protected would promote efforts towards environmental and marine biodiversity protection in the West Philippine Sea or South China Sea.

"We are now looking into the possibility of declaring Pag-asa Island and Eastern Kalayaan as Marine Protected Areas. These areas are within the Philippine Exclusive Economic Zone," Esperon said in a statement released Wednesday.

He pointed out that the Bureau of Fisheries and Aquatic Resources had declared Taklobos as endangered species.

"The Taklobos are part of the ecosystem that sustains the food security not only for the Filipinos, but for the world's people, as well," the National Security Adviser said.

The Cabinet official noted that the Philippine government had taken diplomatic and legal actions to address illegal fishing, poaching and environmental abuse in the West Philippine Sea.

On the presence of Chinese fishing boats in the vicinity of Pag-asa Island and nearby islands, Esperon said the government continues to monitor the presence of foreign vessels in the area.

Hundreds of Chinese vessels, believed to be part of China's maritime militia, were seen loitering in the area of Pag-asa Island while the Philippines conducts rehabilitation efforts on the island, which is one of the largest features in the Spratly chain.

Echoing the Department of Foreign Affairs' previous statement, Esperon pointed out that the presence of Chinese vessels in Philippine waters, whether for military, fishing or other purposes, is "illegal and a clear violation of our sovereign rights and economic jurisdiction as defined in the UNCLOS."

"We maintain that the Kalayaan Island Group, and all the features in the West Philippine Sea, are subject to the effective and exclusive control and management of the Philippines," Esperon said.

The Philippines will undertake diplomatic actions on illegal activities in the country's exclusive economic zone.

Esperon also mentioned that this might be brought up in the scheduled bilateral meeting between President Rodrigo Duterte and Chinese President Xi Jinping on the sidelines of the second Belt and Road Forum in Beijing this week.

The Duterte administration will also "remain steadfast" on the 2016 ruling of a United Nations-backed tribunal on the South China Sea dispute.

Almost three years ago, the arbitral tribunal ruled that China violated its commitment under the UNCLOS upon constructing artificial islands in the Philippines' exclusive economic zone.

"Even as we pursue friendly and diplomatic relations with other nations, the Philippines' sovereign rights remains non-negotiable. We will continue to assert our rights over the territorial seas, guided by the Arbitral award, the irreversible and permanent statutes of international law, including the UNCLOS," Esperon said.