Two US aircraft carriers have carried out drills in the South China Sea, a US Navy spokesman said Saturday, after the Pentagon expressed concerns over Chinese military exercises around a disputed archipelago. The USS Nimitz and USS Ronald Reagan conducted dual carrier operations in the waterway to “support a free and open Indo-Pacific,” the spokesman said. The drills came as the Pentagon said it was “concerned” about Chinese military exercises in the South China Sea, warning the manoeuvres will “further destabilise” the region.