Beijing on Monday said that Washington was playing “an extremely ignoble role” in backing Manila in the disputed South China Sea, days after the Philippine leader warned of a red line — what it would consider “an act of war” — in the strategic waterway.

“Driven by selfish geopolitical calculations, the U.S. has played an extremely ignoble role by supporting and assisting the Philippines in infringing on China’s sovereignty, and by exploiting the South China Sea issue to drive a wedge between China and other regional countries,” a spokesperson for China’s Foreign Ministry said in response to a speech by Philippine President Ferdinand Marcos Jr.

In the keynote address Friday at the Shangri-La Dialogue in Singapore, Marcos 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.”