The tweet criticised China for seizing a US Navy underwater drone in the South China Sea. He initially wrote "unprecedented" incorrectly in the tweet (spelling it as "unpresidented"), but later corrected his mistake.
China steals United States Navy research drone in international waters - rips it out of water and takes it to China in unprecedented act.— Donald J. Trump (@realDonaldTrump) December 17, 2016
The U.S. defence department has called for China to return the drone, also known as an unmanned underwater vehicle (UUV). The equipment was being used by a survey ship, USNS Bowditch, when it was taken.
Pentagon press secretary Peter Cook said in a statement: "The USNS Bowditch 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."
The Chinese defence ministry has said that its navy had picked up the drone "to prevent it endangering the ship's navigation and crew" and that it will be returned to the U.S. "in an appropriate manner".
The move from China comes after Trump called the president of Taiwan and reportedly said he would change U.S. policy over the island if China did not work with the U.S. on other disputes, such as the South China Sea.