A pair of U.S. B-52 Stratofortress bombers conducted another show of force near contested airspace by man-made islands in the South China Sea, U.S. Pacific Air Forces confirmed Tuesday.

The flight took place early Tuesday and involved two bombers flying from the U.S. base at Diego Garcia.

“Two B-52H Stratofortress bombers departed Navy Support Facility, Diego Garcia, on a routine mission, conducting training in the vicinity of the South China Sea prior to returning to Diego Garcia, June 5,” the command said in a statement.

The overflight was the latest by U.S. strategic bombers to assert that the waterways and airspace around and above a series of Chinese man-made islands in the South China Sea remain open. China has made territorial claims on the waters and airspace surrounding its builds.

The flight comes about a week after the U.S. sent guided-missile destroyer Higgins and the guided-missile cruiser Antietam within 12 nautical miles of the contested South China Sea Paracel Islands and uninvited China from a massive, multi-national Rim of the Pacific naval exercise. It also comes directly after Defense Secretary Jim Mattis used a major security conference in Singapore to call out China for instigating “intimidation and coercion” though its militarization of the islands and economic pressures it exerts in the region.

Tuesday’s flight, which Pacific Air Forces said was a training mission, is part of the “continuous bomber presence missions ... intended to maintain the readiness of U.S. forces,” the command said.