Washington (Reuters): US officials claimed that a Chinese warship has seized an underwater US drone deployed to survey oceanographic ship in the South China Sea, triggering a formal diplomatic protest and a demand for its return.

US officials said that the drone was taken by Chinese warship, the first seizure of its kind in recent memory, about 50 nautical miles northwest of Subic Bay off the Philippines just as the USNS Bowditch was about to retrieve the unmanned underwater vehicle (UUV).

An official said, speaking on condition of anonymity "The UUV was lawfully conducting a military survey in the waters of the South China Sea."

The official said "It's a sovereign immune vessel, clearly marked in English not to be removed from the water - that it was U.S. property."

The Pentagon confirmed the incident at a news briefing and said the drone used commercially available technology and sold for about $150,000.

Still, the Pentagon viewed China's seizure seriously since it had effectively taken U.S. military property.

Pentagon spokesman Jeff 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."

Senator Ben Cardin, the top Democrat on the U.S. Senate Foreign Relations Committee, called the seizure "a remarkably brazen violation of international law."

U.S. Navy Secretary Ray Mabus cited a "growing China" as one of the reasons that the Navy needed to expand its fleet to 355 ships, including 12 carriers, 104 large surface combatants, 38 amphibious ships and 66 submarines.

The seizure will add to concerns about China's increased military presence and aggressive posture in the disputed South China Sea, including its militarization of maritime outposts.