A US official said "we would like it back, and we would like this not to happen again"
A Chinese warship has seized a US Navy underwater drone collecting scientific data in the South China Sea, according to the Pentagon.
The US is demanding Beijing returns the unmanned gilder and has issued a formal complaint.
The drone was one of two being recovered by a US survey ship about 50 nautical miles northwest of Subic Bay near the Philippines when the Chinese warship approached.
The Dalang Class Chinese ship sent out a small boat which then took one of the drones, said a Pentagon spokesman.
Navy Captain Jeff Davis told reporters: "It is ours. It's clearly marked as ours. We would like it back, and we would like this not to happen again."
He said the Chinese ship acknowledged radio messages from the US ship, but did not respond to demands that the glider be returned.
The Navy oceanographic survey ship, USNS Bowditch which is armed, was stopped in the water when the Chinese ship approached and the vessels were about 500 metres apart.
Captain Davis said no shots were fired, and as the Chinese ship left with the drone its only radio response to the US vessel was: "We are returning to normal operations."