China's Maritime Safety Administration announced on June 25, 2015, that the US$ 1 billion oil-rig the 'Haiyang Shiyou 981' rig would carry out "ocean drilling operations" 75 nautical miles south of the resort city of Sanya on southern Hainan island. The CNOOC could not be reached for comment on June 26. Experts estimate the drilling site is about 104 miles (167 km) east of the Vietnam coast and that the rig will remain there from June 25 until August 20, 2015. The oil rig was deployed in the area last year too. The website of the country's state-controlled Tuoi Tre newspaper on June 26, 2015, quoted unidentified sources as saying Vietnam's maritime authorities were monitoring the rig's placement. The rig movement comes weeks before Vietnam's top leader, Nguyen Phu Trong, is expected to visit the United States, in the first such trip by a general secretary of the nation's Communist Party and amid rising concerns at China's rapid creation of artificial islands on South China Sea reefs.