



According to the Pentagon, as the Chinese ship left with the drone, which is about 10 feet long, its only radio response to the U.S. vessel was, "We are returning to normal operations."



Bonnie Glaser, senior adviser for Asia at the Center for Strategic and International Studies, said the seizure of the glider occurred inside the exclusive economic zone of the Philippines, not China, and appeared to be a violation of international law.



China delineates its South China Sea claims with a roughly drawn sea border known as the "nine-dash line" that runs along the west coast of the Philippines. However, it hasn't explicitly said whether it considers those waters as sovereign territory, and says it doesn't disrupt the passage of other nations' shipping through the area. The U.S. doesn't take a position on sovereignty claims, but insists on freedom of navigation, including the right of its naval vessels to conduct training and other operations in the sea.



Davis said that the incident could be the first time in recent history that China has taken a U.S. naval vessel. Some observers have called it the most significant dispute between the sides' militaries since the April 2001 midair collision between a U.S. Navy surveillance aircraft and a Chinese fighter jet about 70 miles from China's Hainan island that led to the death of a Chinese pilot.



The drone seizure seemed likely to fray the already tense relations between U.S. and China. Beijing was angered by Trump's decision to talk by phone with Taiwanese President Tsai Ing-wen on Dec. 2, and by his later comments that he did not feel "bound by a one-China policy" regarding the status of Taiwan, unless the U.S. could gain trade or other benefits from China. China considers the self-governing island its own territory to be recovered by force if it deems necessary.



There also have been increased tensions over Beijing's ongoing military buildup in the South China Sea, mainly the development and militarization of man-made shoals and islands aimed at extending China's reach in the strategically vital area, through which about $5 trillion in global trade passes annually.