With Manila’s relations with Beijing sliding into dangerous territory, Philippine President Ferdinand Marcos Jr. has warned Beijing that if a Philippine citizen were to be deliberately killed in a clash with the China Coast Guard, this would be “very close to what we define as an act of war.”

Should the incidents in the South China Sea get to that point, “we would have certainly crossed the Rubicon,” Marcos said Friday in response to a question after delivering a keynote speech to kick off this year’s IISS Shangri-la Dialogue security conference in Singapore.

“Is that a red line? Almost certainly. It's going to be a red line,” added the Philippine leader, warning that Manila would respond “accordingly” while its treaty ally, the United States, would hold “the same standard” and support the Philippines in any joint action.