The Pentagon says a Chinese warship has seized an unmanned U.S. Navy underwater glider that was collecting unclassified scientific data in the South China Sea.
Pentagon spokesman Jeff Davis says the United States has issued a formal diplomatic complaint about the incident and is asking for the return of the underwater drone.
Davis said a U.S. Navy ship was recovering two unmanned gliders about 85 kilometers northwest of a U.S. naval base in the Philippines when the Chinese warship approached and took one of the small drone vessels.
He said the Chinese ship acknowledged radio messages from the U.S. ship but did not respond to demands for the small vessel to be returned.
U.S. officials say the drone -- about 3 meters long and less than 1 meter wide – was lawfully conducting a military survey in the waters of the South China Sea.
They described the drone as a "sovereign immune vessel, clearly marked in English not to be removed from the water" and saying that it is U.S. property.
The Pentagon later confirmed that the value of the drone is about $150,000.
Davis said: "It is ours, and it is clearly marked as ours and we would like it back. And we would like this not to happen again."
China's embassy in Washington said it had no immediate comment about the incident, which is likely to fray already tense relations between the United States and Beijing.
China in recent years has been building up military maritime outposts in the South China Sea.
Beijing was angered by U.S. President-elect Donald Trump's decision to talk by phone with Taiwanese President Tsai Ing-wen on December 2.
Trump also has said he does not feel "bound by a one-China policy" regarding the status of Taiwan, unless the United States gains trade or other benefits from Beijing.
China claims that most of the South China Sea is its own territorial waters -- a position that has led to maritime territorial disputes with Vietnam, Malaysia, the Philippines, Taiwan, and Indonesia.
China’s government has estimated the South China sea may contain some 17.7 billion tons of crude oil.