China Seizes U.S. Underwater Drone From International Waters, Pentagon Says

China has seized an unmanned underwater vehicle deployed by a U.S. Navy ship in international waters, according to Pentagon officials.

The seizure of the underwater vehicle took place Thursday, about 50 nautical miles northwest of Subic Bay in the Philippines, Pentagon Press Secretary Peter Cook said in a statement Friday.

The situation is unusual: U.S. Navy Capt. Jeff Davis told journalists there was no precedent for it in recent memory, NPR's Tom Bowman reports.

The Pentagon said the USNS Bowditch, an oceanographic survey ship, had two unclassified "ocean gliders" — unmanned underwater vehicles (UUVs) — in the water, conducting "routine operations in accordance with international law." The undersea drones measure things such as salinity and temperature.

The Bowditch was retrieving one vehicle when a Chinese warship pulled up, put a small boat in the water and retrieved the second UUV, officials told reporters.

The U.S. sent radio messages requesting that the drone be returned, the Pentagon statement said, but the Chinese ship merely acknowledged the messages and ignored the request.

No shots were fired by either vehicle, officials said, and the Chinese ship left with a final message that it was returning to normal operations — and with the drone.

The U.S. has issued a demarche — a formal diplomatic protest — and demanded the drone's return, Reuters reports.

"We call upon China to return our UUV immediately, and to comply with all of its obligations under international law," Pentagon Press Secretary Peter Cook said in his statement.

The incident occurred in the long-disputed waters of the South China Sea, where several countries have various overlapping territorial claims. China has been the most aggressive in claiming the strategically and economically significant waters as its own.

Competing Claims In The South China And East China Seas Notes These are the approximate claims by China and other countries. In many cases, countries are intentionally vague about the extent of their claims.

Satellite photos taken in the past few weeks appear to show a significant defense buildup on China's artificial islands in the South China Sea. Beijing uses the artificial islands as part of the justification for China's territorial claims — which were invalidated months ago by an international tribunal in The Hague, Netherlands.

That ruling is "legally binding, but all but impossible to enforce," as NPR's Anthony Kuhn put it at the time.

"The U.S. has consistently said it has no dog in the fight over conflicting claims in the South China Sea," Michael Sullivan reported for NPR this summer. "But ... the U.S. has conducted a series of high-profile freedom of navigation operations in the disputed waters, near the artificial islands China has created there."

The drone seizure also comes amid fresh tensions between China and the U.S., following moves by President-elect Donald Trump that have unsettled decades of diplomatic protocol.

Trump spoke with Taiwan's president by phone earlier this month, and told Fox News he "wouldn't feel bound by a one-China policy" — the policy holding that Taiwan is part of China, which China considers essential for diplomatic relations. China responded to Trump's latter comments by expressing "serious concerns."

NPR's Rob Schmitz wrote last month that it's hard to tell how Trump's presidency will affect ties with China, which has been spending "more than ever" to expand its military capabilities.

He noted that one Trump adviser said Trump would beef up the U.S. fleet to defend U.S. trade in the South China Sea — which directly conflicts with Trump's campaign rhetoric.

The drone incident also could impact diplomatic relations with the Philippines.

The U.S. and the Philippines, a former U.S. colony, have been closely tied for decades; the two countries are treaty allies. In recent years, a rise in tensions between Manila and Beijing has led to a growing U.S. military presence in the Philippines.

But the Philippines' new president, Rodrigo Duterte, has signaled a shift away from the U.S. and made overtures to China.

"There's no doubt Duterte is trying to reset the Philippines' fractious relationship with China, a falling-out based largely on Beijing's recent territorial moves in the South China Sea," Michael Sullivan reported for NPR this fall. "But there's also little doubt that Manila's relationship with Washington is on the rocks — and not just because of U.S. criticism of Duterte's war on drugs, which has left more than 3,000 dead since the president took office in June."

One expert told Sullivan that there's widespread belief in the Philippines that the U.S. commitment to the Philippines is "limited," and would not extend to substantive assistance for Manila in a real conflict with Beijing.