Vietnam warned China on Tuesday against drilling in disputed waters in the South China Sea after Beijing steered an oil rig that was the subject of a previous standoff into an area where jurisdiction is unclear.
Vietnam closely tracks the movement of the oil rig, which in mid-2014 caused the pair's worst diplomatic breakdown in decades when China parked it for 10 weeks in waters Vietnam considers its own.
The communist neighbors share more than $60 billion in annual trade, but anti-China sentiment is strong in Vietnam, where people remain embittered over what many see as a history of Chinese bullying and territorial infringements in the South China Sea.
Vietnam's Foreign Ministry spokesman, Le Hai Binh, said in a statement that the rig had moved on Saturday to a location where both countries' continental-shelf claims overlap.
"Vietnam requests China does not conduct drilling actions and withdraw Hai Duong 981 from this area," Binh said, referring to the rig by its Vietnamese name. "Vietnam reserves all legal rights and interests to this area, which are in accordance with international laws."
There was no immediate response to requests for comment from China, where the $1 billion deep-water rig is known as Haiyang Shiyou 981.
Vietnam's concern over the rig follows its complaints, echoed also by the Philippines, over recent test flights by China on an artificial island in the disputed Spratly archipelago.
China considers most of the South China Sea to be under its jurisdiction, but Brunei, Malaysia, the Philippines, Taiwan and Vietnam have competing claims. About $5 trillion in ship-borne trade passes through the waters each year.
Separately on Tuesday, demonstrators held a rare anti-China protest in Hanoi to mark the 42nd anniversary of China taking full control of the disputed Paracel Islands.