A US military surveillance aircraft was spotted close to China’s south coast for the third time this week on Friday, Chinese sources said, as the US Navy reported two of its aircraft carrier strike groups had conducted dual exercises in the South China Sea to boost their combat readiness. The US Air Force E-8C aircraft, which is fitted with specialist radar, communications, operations and control systems, was seen reconnoitring as close to 72 nautical miles off the coast of Guangdong province, according to the South China Sea Strategic Situation Probing Initiative, a think tank based at Peking University. The sighting was the third this week, it said. Analysts said the plane was probably monitoring Chinese troop deployments and movement along the coast. The think tank said also that a US Air Force E-3 Sentry early warning and control aircraft, which provides all-weather surveillance, command, control and communications, was spotted over the South China Sea. Also on Friday, the US Navy said two of its aircraft carrier strike groups had conducted dual exercises in the South China Sea to boost their combat readiness. The groups, led by the USS Nimitz and USS Ronald Reagan, were showing their “operational commitment to allies and partners in the region, providing combatant commanders with significant operational flexibility if needed in response to regional situations”, according to a report published on Friday on cpf.navy.mil, a news portal for the US Navy. Rear Admiral Jim Kirk, commander of the Nimitz strike group, was quoted as saying the warships had been “operating in the South China Sea, wherever international law allows, to reinforce our commitment to a free and open Indo-Pacific, a rules based international order, and to our allies and partners in the region”. The two groups conducted tactical air defence exercises to maintain combat readiness, the report said, adding that they trained “to the highest levels of readiness to ensure responsiveness to any contingency through power projection”. “Security and stability is essential to peace and prosperity for all nations, and it is for that reason the US Navy has been present and ready in the Pacific for over 75 years,” Kirk said. The US Navy said on July 4 that the two aircraft carrier strike groups had been deployed to the South China Sea “in support of a free and open Indo-Pacific”, while Chinese forces were staging a drill near the Paracel Islands, which are claimed by mainland China, Taiwan and Vietnam. On July 10, the defence ministry in Beijing lambasted the deployment , claiming the US had “carried out navigational hegemony” through its repeated deployments of warships to the region and describing Washington as the biggest driver of militarisation in the strategic waterway. Kirk’s comments on the latest naval activity came after US Secretary of State Mike Pompeo said the US formally opposed Beijing’s territorial claims within the so-called nine-dash line that encompasses almost all of the South China Sea – in line with a 2016 ruling by an international tribunal at The Hague. His remarks may embolden Southeast Asian nations to assert their maritime claims to the disputed waters but observers say most are unlikely to openly choose sides between the US and China. Collin Koh, a research fellow at the S Rajaratnam School of International Studies at Singapore’s Nanyang Technological University, said the carrier strike groups’ operations showed the US Navy was intent on maintaining its freedom of navigation in the South China Sea regardless of the rising challenge from the Chinese military. “The US Navy remains operationally ready and has been able to bring the Covid-19 contagion under control,” he said. “The intended audience of such signalling isn’t just China, but also other regional governments to underline continued US security commitments.”