China’s Foreign Minister Wang Yi says the country will maintain military pressure on the Philippines amid a dispute over sovereignty in the South China Sea that could involve U.S. forces defending their treaty partner.

In a phone conversation Wednesday with his Philippine counterpart, Enrique A. Manalo, Wang “warned that if the Philippine side misjudges the situation, goes its own way, or even colludes with ill-intentioned external forces to continue to stir up troubles, China will defend its rights in accordance with law and respond resolutely,” the official Xinhua News Agency reported.

Wang’s comments follow China’s mobilization of its coast guard and maritime militia to block Philippine supply missions to support its soldiers and fishermen. China claims sovereignty over virtually the entire South China Sea, one of the world’s most crucial waterways for shipping, putting it at odds with the Philippines, Vietnam, Malaysia, Taiwan and Brunei, who all maintain claims over islands, reefs and undersea resources in the region.