The United States on Friday called Chinese actions in using water cannon against Philippine resupply boats in the South China Sea "dangerous, provocative, and unjustified," and warned that an armed attack on Philippine vessels would invoke U.S. mutual defense commitments.

State Department spokesman Ned Price said Washington stood by its treaty ally the Philippines amid an "escalation that directly threatens regional peace and stability."

Beijing "should not interfere with lawful Philippine activities in the Philippines’ exclusive economic zone," he said in a statement.