Two US warships are operating in the South China Sea, the Navy said on Tuesday, with three regional security sources saying they were near an area of a stand-off between China and Malaysia. The Haiyang Dizhi 8, a Chinese government research ship, was spotted last week conducting a survey close to an exploration vessel operated by Malaysia’s state oil company Petronas, months after it undertook a similar patrol off Vietnam. The incident prompted the United States to call on China to stop its “bullying behaviour” in the disputed waters, citing concern over Beijing’s provocative actions towards offshore oil and gas developments there. The Malaysian exploration triggered a flurry of patrols and presence operations by China Coast Guard and maritime militia ships, Vietnamese maritime militia ships and ships of the Royal Malaysian Navy and Malaysian Maritime Enforcement Agency (also known as the Malaysian Coast Guard). China Coast Guard ships have also been maintaining a continuous presence at the Luconia Shoals, which lies in Malaysia’s Exclusive Economic Zone and is also claimed by China. These ships have also made patrols close to Malaysian oil platforms in Malaysia’s EEZ. Despite all the activity, no at-sea incidents have been reported, and all three governments are content to keep matters out of the public eye. China has denied reports of a stand-off, saying that the Haiyang Dizhi 8 was conducting normal activities.