MANILA - The Department of Foreign Affairs on Monday said it was "closely monitoring" the situation in South China Sea, after Beijing landed bombers on islands and reefs in the disputed region as part of a training exercise.

"The Department of Foreign Affairs, in close coordination with the other relevant departments and agencies, is closely monitoring developments in the West Philippine Sea and the South China Sea," the agency said in a statement.

"We are taking the appropriate diplomatic action necessary to protect our claims and will continue to do so in the future. We reiterate our commitment to protect every single inch of our territory and areas which we have sovereign rights over," it added.

China's air force said Friday it conducted take-off and landing training on in the strategic waterway "to improve our ability to 'reach all territory, conduct strikes at any time and strike in all directions.'"

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The United States has dispatched warships to disputed areas of the South China Sea in a bid to challenge Beijing's extensive sovereignty claims in the territory, which is subject to various claims by China, Vietnam, the Philippines, Taiwan, Brunei, and Malaysia.

President Rodrigo Duterte has maintained a soft stance on the Philippines' maritime dispute with China since assuming office. He has repeatedly stressed that antagonizing China would not do Manila any good, as it cannot match the Asian superpower’s military power.

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The DFA, in its statement, said that "appropriate language, whether expressions of condemnation or concern, over certain developments are clearly conveyed through diplomatic channels."

The agency, however, said "it is not our policy to publicize every action" taken by the government.

It also said it eyes a comprehensive Code of Conduct promoting cooperation in the region.

China has said its military facilities in the Spratlys are purely defensive, and that it can do what it likes on its own territory.

Some Filipino opposition lawmakers condemned China's militarization of the South China Sea and what they said was the inaction of their own government.

Senator Risa Hontiveros sought an end to Manila's "subservience" to China, while Magdalo party-list Rep. Gary Alejano said the issue of China's militarization in the South China Sea is a "global concern."

President Rodrigo Duterte, meanwhile, defended his position not to confront China and reiterated his openness to undertake joint exploration and development in waters believed to be rich in oil and natural gas.

"You know they have the planes, not stationed in Spratlys but near the provinces facing -- Chinese provinces facing the Spratlys and the China Sea," he said in a speech late Saturday.

It was not clear if he was aware of the news about China's bombers landing on islands and reefs in the South China Sea.

With a report from Reuters