President-elect Donald Trump made it clear on Saturday that China’s seizure of a U.S. Navy drone in international waters was "stolen" and an "unprecedented act."

Trump tweeted the message Saturday morning saying, “China steals United States Navy research drone in international waters - rips it out of water and takes it to China in unprecedented act.”

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

A U.S. vessel had its underwater drone stolen by a Chinese warship "literally right in front of the eyes of the American crew" on Thursday, a Department of Defense official told CNN Friday.

The USNS Bowditch was sailing near the South China Sea when it stopped in the water to pick up two underwater drones. Suddenly, a Chinese war ship that had been shadowing the Bowditch put a small boat into the water. The small boat then came up alongside the U.S. ship and took one of the drones. The U.S. vessel tried to plead with the Chinese ships but received no response, the official said.