Vietnam warned China on Tuesday against drilling in "undelineated" waters in the East Sea, after Beijing steered an oil rig at the center of a previous stand-off between the countries into a stretch 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 claimed by Vietnam.
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 shelves overlap.
"Vietnam requests China does not conduct drilling actions and withdraw Hai Duong 981 from this area," Binh said, referring to the rig by the 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 follow its complaints, echoed also by the Philippines, over recent test flights by China on an artificial island in the disputed Spratly archipelago.