Two U.S. bombers flew over the South China Sea on Friday as President Trump and China’s President Xi Jinping prepare for a possible meeting on the sidelines of the G-20 summit in Germany.

The U.S. Air Force said in a statement the two B-1B Lancers made the flight from after training with Japanese jet fighters in the East China Sea, according to Reuters.

"This is a clear demonstration of our ability to conduct seamless operations with all our allies," U.S. Air Force spokesman Maj. Ryan Simpson said.

China has made claims to nearly all of the South China Sea, which holds strategic international shipping routes. About $5 trillion of shipping trade passes through the region every year, according to Reuters. Beijing’s claims in the region have been contested by Brunei, Malaysia, Philippines, Taiwan and Vietnam.

The flight is the latest challenge from the U.S.

The USS Stethem, a guided-missile destroyer based in Japan, sailed within 12 nautical miles of Triton Island, which is part of the Paracel Islands in the South China Sea. It was the second time the Trump administration had made a freedom of navigation patrol since taking office in January.