Beijing, China - Beijing has taken a swipe at the US for what it calls "selfish geopolitical calculations" amid continuing tensions between China and the Philippines in the South China Sea.

Beijing's strongly-worded threats follow a keynote address by the Philippines' President Ferdinand "Bongbong" Marcos Jr. at the Shangri-La Dialogue in Singapore, in which he warned that the killing of a Filipino mariner in coastal clashes would cross a "red line" for Manila.

"That would certainly increase the level of response, and if by a willful act a Filipino not only serviceman, but Filipino citizen [is killed], that would come very close to what we define as an 'act of war,'" Marcos said in response to journalist questions after his speech.

"We have already suffered injury, but thank god we have not yet gotten to the point where any of our participants, civilian or otherwise, have been killed. But once we get to that point... we would have crossed the Rubicon. Is that a red line? Almost certainly it's going to be a red line."

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Following the speech, a spokesperson for the Chinese Foreign Ministry lashed out at the Philippines, saying that it had "breached its commitments and the common understandings with China" during recent escalation in the South China Sea.

Specifically, the foreign ministry said "the so-called arbitral award on the South China Sea is illegal, null and void. Without the Chinese government’s prior consent, the Philippines unilaterally initiated an international arbitration, which violated international law."

The Chinese spokesperson also took aim at the US, insinuating that the Philippines' foreign policy is being dictated by Washington and asking, "Whose bidding is the Philippines doing with all these maritime actions?"

"Driven by selfish geopolitical calculations, the US has played an extremely ignoble role by supporting and assisting the Philippines in infringing on China’s sovereignty," the spokesperson said. "And by exploiting the South China Sea issue to drive a wedge between China and other regional countries.”

"Countries in the region need to stay vigilant and always make sure that they themselves are the ones sitting in the driver’s seat when it comes to the peace and stability of the South China Sea."

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Chinese threats on Monday followed complaints over the weekend that support for Taiwanese independence were "salami slicing tactics," mere weeks after China encircled the island nation with military vessels and aircraft in May.

On Saturday, US Secretary of Defense Lloyd Austin tried to cool down tensions between the Philippines and China, saying that a "war or a fight with China is neither imminent, in my view, nor unavoidable."