Jose Manuel Romualdez, Philippine ambassador to the United States, said in an online briefing that the agreement will stipulate the exercises are aimed to "deter any kind of aggression" in the South China Sea and preserve the freedom of navigation in the sea.

The remarks come as the three countries plus Australia are set to hold their first full-scale naval exercise Sunday, according to multiple government sources. The quadrilateral drill, which will include anti-submarine warfare training, will be held within the Southeast Asian country's exclusive economic zone, the sources have said.

Philippine President Ferdinand Marcos Jr., Japanese Prime Minister Fumio Kishida and U.S. President Joe Biden will meet in Washington on April 11. Marcos has said that the three leaders are expected to forge an agreement that will add more structure to the three countries' interoperability and joint cruises.

Romualdez said the leaders will also discuss cooperation in such fields as digital transformation and the supply chain of semiconductors, with economic security being "the only way to counter any kind of economic coercion."

Regarding the regular maritime exercises, Romualdez said, "We're also inviting other countries, like-minded countries like Australia, to join in on this particular effort."

Romualdez added that a General Security of Military Information Agreement between his country and the United States will be signed soon, while a similar intelligence-sharing agreement with Japan is "on the table."