WASHINGTON (AP) — China’s blocking of supplies to a Philippine outpost in the South China Sea is “provocative” and raises tensions, the United States said Wednesday, in its latest criticism of China’s assertive conduct in disputed seas of East Asia.

The Philippines, a U.S. ally, protested to China Tuesday its prevention of two Filipino vessels from taking supplies to troops on a decrepit military hospital ship that ran aground 15 years ago on the shallow coral outcrop of the Second Thomas Shoal. The rusty ship has since become the symbol of Philippine sovereignty over the area.