The United States and China are in a fresh row over the alleged seizure of a US underwater drone by a Chinese navy warship in the international waters in the South China Sea.
The US has demanded that China "immediately" return its underwater drone, ''unlawfully'' seized by Chinese navy in international waters in the South China Sea.
The incident occurred on 15 December, in the Subic Bay, about 100 miles from a nearby port, US defence officials said on Friday.
The drone was used by USNS Bowditch, an oceanographic vessel operating in the region, for collecting data in international waters in the South China Sea, officials said.
The Chinese warship, a Dalang III-class vessel (ASR-510), seized the UUV in full view of the American ship, just as the ship was about to retrieve the unmanned underwater vehicle (UUV), which was mapping the sea floor and collecting oceanographic data, US officials said.
"Using appropriate government-to-government channels, the Department of Defence has called upon China to immediately return an unmanned underwater vehicle (UUV) that China unlawfully seized on December 15 in the South China Sea while it was being recovered by a US Navy oceanographic survey ship," Pentagon press secretary Peter Cook said.
The USNS Bowditch (T-AGS 62) and the UUV - an unclassified "ocean glider" system used around the world to gather military oceanographic data such as salinity, water temperature, and sound speed - were conducting routine operations in accordance with international law about 50 nautical miles northwest of Subic Bay, Philippines, when a Chinese Navy PRC DALANG III-Class ship (ASR-510) launched a small boat and retrieved the UUV, he said.
The USNS Bowditch (T-AGS 62) is owned by the US Navy but operated by Military Sealift Command around the world to gather military oceanographic data such as salinity, water temperature, and sound speed.
''The ship ''supports worldwide oceanography programs, including performing acoustical, biological, physical and geophysical surveys,'' according to the website.
The Chinese naval vessel allegedly slowed Bowditch and used a smaller craft to retrieve the drone. The US ship informed the Chinese crew that the vessel was US property; but, did not receive a response from the Chinese, says a CNN report.
The Pentagon said, its only radio response to the US vessel was, ''We are returning to normal operations.''
The US Department of State lodged a formal protest Friday and officially demanded the return of the drone, a Slocum Glider worth $150,000.
"Bowditch made contact with the PRC Navy ship via bridge-to-bridge radio to request the return of the UUV. The radio contact was acknowledged by the PRC Navy ship, but the request was ignored," he said.
"The UUV is a sovereign immune vessel of the US. We call upon China to return our UUV immediately, and to comply with all of its obligations under international law," Cook demanded.
Senator Ben Cardin of the Senate Foreign Relations Committee termed the China's seizure of an US Navy unmanned scientific research submersible in international waters off the South China Sea as a remarkably brazen violation of international law.
"No matter its motivation, China needs to explain its actions and immediately return the undersea drone, untampered with, to the United States," he said.
"China's increasingly aggressive behaviour in the South China Sea - including the militarisation of the artificial features that it has built in the region, in direct contradiction of a pledge made by President Xi Jinping not to do so - is deeply disturbing, and not consistent with the actions of a nation seeking to build a constructive and cooperative relationship with the United States," Cardin said.
"The United States has a deep and abiding interest in freedom of navigation and the free-flow of commerce in the Asia-Pacific region, and a steadfast commitment to our regional allies and partners in maintaining stability, security and the rule of law, including safe passage in international waters," Cardin said.
The incident comes amid assertive Chinese actions in the South China Sea, including installation of weapon systems in the disputed islands.