The guided-missile destroyer John S. McCain crossed through the South China Sea, passing near the disputed Paracel Islands, on Friday.
Beijing is doubling down on its assertion of total control over the South China Sea, swarming warships and aircraft around a US destroyer as it sailed through international waters at the weekend.
The warship's presence is part of Washington's ongoing "Freedom of Navigation" campaign to assert what it calls common practice.
The post-World War II Law of the Sea determines the South China Sea and Taiwan Strait to be international waters.
He warned of tougher measures to come, stating Beijing would take "all necessary" measures to safeguard its national security.
Ruling aside, China insists its alleged sovereignty makes it illegal for foreign militaries to send vessels and aircraft through these waters without permission. »