A Chinese Navy warship has seized an underwater drone deployed by an American oceanographic vessel in international waters in the South China Sea, triggering a formal diplomatic protest from the US and a demand for its return, a US defence official said. <br/><br/>The naval glider was used to test water salinity and temperatures to help in the mapping of underwater channels, the official said, before adding it was taken by China in international waters about 50 miles off Subic Bay. <br/><br/>The incident took place on Thursday just as the USNS Bowditch, an oceanographic survey ship, was about to retrieve the unmanned, underwater vehicle, the official said.<br/><br/>The Philippines, Brunei, Malaysia and Vietnam have competing claims in the South China Sea, which is laced with the world's most heavily travelled international trade routes.

A Chinese Navy warship has seized an underwater drone deployed by an American oceanographic vessel in international waters in the South China Sea, triggering a formal diplomatic protest from the US and a demand for its return, a US defence official said. <br/><br/>The naval glider was used to test water salinity and temperatures to help in the mapping of underwater channels, the official said, before adding it was taken by China in international waters about 50 miles off Subic Bay. <br/><br/>The incident took place on Thursday just as the USNS Bowditch, an oceanographic survey ship, was about to retrieve the unmanned, underwater vehicle, the official said.<br/><br/> The Philippines, Brunei, Malaysia and Vietnam have competing claims in the South China Sea, which is laced with the world's most heavily travelled international trade routes.