THE Pentagon says a Chinese warship has seized a US Navy underwater drone collecting unclassified data in international waters in the South China Sea.
The incident has prompted a formal démarche from the United States and a demand for its return.
It is the first such seizure in recent memory and took took place on 15 December northwest of Subic Bay, just as the USNS Bowditch - an oceanographic survey ship - was about to retrieve the unmaned underwater vehicle (UUV), a US official told Reuters.
"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 US property."
Navy Captain Jeff Davis, a Pentagon spokesman, says the US is asking for the drone's return.
The incident is likely to fray the already tense relations between US and China. Beijing was angered by President-elect Donald Trump's decision to talk by phone with Taiwanese President Tsai Ing-wen earlier this month, and by his later comments that he did not feel "bound by a 'One China' policy" regarding the status of Taiwan, which has been US policy for decades.
Captain Davis says a civilian US Navy ship operated by the military's Sealift Command was recovering two of the unmanned gliders about 50 miles northwest of Subic Bay near the Philippines when the Chinese ship approached and took one of the small vessels. He says the Chinese ship acknowledged radio messages from the US ship, but did not respond to demands the glider be returned.
The Chinese have acknowledged the démarche but not responded to it.
"It is ours. It's clearly marked as ours. We would like it back, and we would like this not to happen again," said Captain Davis
The seized underwater drone was part of an unclassified program to collect oceanographic data, including salinity, temperature and clarity of the water, according to the official. Such data can help inform US military sonar data.
The incident will add to concerns about China's growing military presence in the disputed South China Sea. The Center for Strategic and International Studies (CSIS), a US security think tank, said in a report late on Wednesday that China appears to have installed anti-aircraft guns and close-in weapons systems designed to guard against missile attack on its seven newly created islands in the disputed sea.
On Thursday the US Pacific fleet said it was ready to confront China should it continue to pursue overreaching maritime claimes in the sea.
Bonnie Glaser, senior adviser for Asia at CSIS, told the Associated Press that the seizure of the glider appeared to occur inside the exclusive economic zone of the Philippines, not China, and appeared to be a violation of international law.
She said China was likely sending a signal to Mr Trump's incoming administration because of his comments about Taiwan. After those comments, Chinese government spokesman An Fengshan said breaching the One China principle "will seriously affect peace and stability across the Taiwan Strait," and undermine relations between Beijing and Washington.
Under the One China policy, the US has long recognised Beijing as China's government and maintains only unofficial relations with Taiwan, a former Japanese colony which broke from the Chinese mainland in 1949. US law requires the government to ensure that the island has the ability to defend itself and to treat all threats to it as issues of national concern.
"My guess is this is not the act of a rogue commander on a Chinese navy ship. We have seen tight control by (Chinese President) Xi Jinping over the military. I'm more inclined to see it as a deliberate act and as a signal," Ms Glaser said. She said China would want Mr Trump "to understand before he is sworn in that the United States can't challenge China's core interests with impunity."
The news also comes as the Philippine foreign secretary said on Friday his country won't take any steps against China in response to the reports on its alleged anti-aircraft and anti-missile weapons in the disputed Sea.
Foreign Secretary Perfecto Yasay Jnr said that while the US and other countries might take actions to ensure freedom of navigation and overflight in the disputed waters, the Philippines will not take any steps that would reignite tensions.
When asked if the Philippine foreign affairs department plans to issue any statement or ask China to clarify, Yasay said, "We want to make sure that there will be no further actions that will heighten the tensions between the two countries, particularly in the Scarborough Shoal."
He was referring to a disputed fishing area off the Philippines' northwestern coast where tensions recently eased after Chinese coast guard ships allowed Filipinos to fish after blocking them from the area for years. China's change of tact came after President Rodrigo Duterte met Mr Jinping in Beijing in October.
Once-hostile ties with China have improved under Mr Duterte, who has reached out to China and Russia while taking a hostile stance toward the US government, which has criticised his bloody crackdown on illegal drugs.
Mr Yasay said in a news conference in Singapore, where he and other officials are accompanying Mr Duterte on a visit, that "there is nothing that we can do about that now, whether or not it is being done for purposes of further militarising these facilities that they have put up.
"We cannot stop China at this point in time and say 'Do not put that up.' We will continue to pursue peaceful means at which all of these can be prevented," he said.
His remarks differed from Defence Secretary Delfin Lorenzana, who expressed concerns over the CSIS report and said the government was attempting to verify it.
"If true, it is a big concern for us and the international community who uses the South China Sea lanes for trade," Mr Lorenzana said on Thursday. "It would mean that the Chinese are militarising the area, which is not good."
Agencies contributed to this report
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