Just days ago, United States sent two of its warships in the disputed waters as it conducted "freedom of navigation", which provoked China and led the latter to warn them off.
Esperonmaintained there is no need to file a diplomatic protest against China over the deployment of its bombers on Woody Island in the South China Sea because it is beyond the Philippine exclusive economic zone.
Amid accusations that the Philippines was not taking advantage of an arbitral ruling that upheld Philippine sovereign rights over disputed territories in the West Philippine Sea, Esperon said, "This Administration does not and will not abandon the ruling of the Permanent Court of Arbitration on the South China Sea disputes".
Though the US' latest freedom of navigation operation was likely planned months in advance, experts said it was suggestive of the US' attempts to pursue a harder line against China in the South China Sea. This comes at a time when the US President Trump seeks to seek Beijing cooperation on North Korea. "We've very open about them, and report them", he said.
"The president has said that".
China thought otherwise, calling the presence of the USA ships unauthorized and provocative.
"If anyone gets the natural resources in the Western Philippines Sea, South China Sea, he will go to war", Cayetano said.
"It's global waters, and a lot of nations want to see freedom of navigation, so we'll continue that", Mattis said.
Cayetano further elaborated that among the territorial issues discussed, with China, were construction activities at a disputed shoal and the unilateral extraction of oil and gas in the region.
Esperon said the Philippines is building five lighthouses on the Kalayaan Group of Islands, a feature of Spratlys in the West Philippine Sea which is claimed by Manila, according to ABS-CBN News.
China says navy pilots aboard the country's sole operating aircraft carrier have completed their first nighttime takeoffs and landings.
However, Cayetano said the president, who has been criticised for his refusal to confront China with the Philippines' 2016 victory at the Hague Tribunal, had warned that he would go to war with Beijing if it broke his "red lines" relating to the South China Sea. The Higgins is one of two U.S warships that sailed through the South China Sea over the weekend.
China claims most of the resources-rich sea through which $5 trillion in shipping trade passes annually, and in recent years has reclaimed reefs and shoals including some claimed by Manila.
But after pounding on the Aquino administration's alleged failures, Cayetano said, "We're not blaming the past administration, some critics are making it appear na iba ang situation ngayon".
Mattis was heading to Hawaii to attend a change-of-command ceremony for the USA military's Pacific Command. He will be replaced by Admiral Philip Davidson.
"We are going out of our way to cooperate with Pacific nations, that's the way we do business in the world", Mattis told reporters traveling with him to a national security conference in Singapore.
Harris has been nominated to become the next US ambassador to South Korea.