The Chinese navy has reportedly seized a U.S. Navy unmanned underwater vehicle (UUV) in the South China Sea, adding a new layer of tension to the two countries’ uneasy relationship. According to several reports, China deployed a boat on Dec. 15 to capture the vehicle in waters 50-100 nautical miles northwest of the Philippines’ Subic Bay port, just before the USNS Bowditch was preparing to retrieve the UUV. U.S. defense officials have said that Washington has requested, through the appropriate diplomatic channels, that Beijing return the vehicle. The incident comes amid increasingly harsh rhetoric between Chinese leaders and the incoming administration of U.S. President-elect Donald Trump, though frictions have been worsening between Washington and Beijing for years as the United States has sought to counter Chinese expansionism in the disputed waters.