SINGAPORE — President Ferdinand Marcos Jr. said that the death of any Filipino citizen due to a "wilful act" is "very, very close to" what the Philippines would consider an "act of war." 

During the question and answer portion of the 2024 IISS Shangri-la Dialogue here in Singapore on Friday evening, an audience member asked Marcos whether a “red line” would be crossed if Chinese Coast Guard ships ended up killing a Filipino sailor.

China has been strongly asserting its territorial rights in the South China Sea since Marcos won the Presidential elections in 2022. But over the past year, tensions between Beijing and Manila have escalated to the point that the Philippine ships have been damaged and hurt Filipino sailors due to water cannon strikes from Chinese ships.

As confrontations continue to strain the relationship between Beijing and Manila, Marcos has sought to strengthen ties with the United States, with whom the Philippines has a mutual defense treaty.

“What would happen if there was an incident that ended up killing a Filipino serviceman, be it a coast guard, or in the military or navy? (If a) Filipino citizen is killed by a willful act, that is I think very, very close to what we define as an act of war, and therefore, we would respond accordingly,” Marcos said.

“Our treaty partners, I believe, also hold that same standard when a joint action will be undertaken in support of any such incident in the Philippines. 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," Marcos added.

Manila and Washington signed the Mutual Defense Treaty (MDT) in 1951, but it has never been clear what conditions would make the deal go into effect.

Marcos said in a media event last month that the MDT between the Philippines and the US would be used if a Filipino soldier was killed in an attack by another country.

Now that he has made it clearer, the MDT would cover even the deaths of fishermen, journalists, and other citizens who were killed by a foreign power.

It was also made public after China announced new rules that would allow the detention of outsiders thought to be trespassing. Beijing wants to claim a lot of space in the South China Sea, and it has accused ships of trespassing even though they are in the Philippines' exclusive economic zone.

Marcos said on 30 May that China's new policy was "worrisome."