Vietnam’s government said it had demanded China to remove an oil exploration rig from the Gulf of Tonkin, an area where the countries are still negotiating a delineation of control, ABC News reported. According to The Wall Street Journal, Vietnam calls on China to stop digging in the disputed offshore zone.

This latest spat comes as relations between the two countries are deteriorating again. Vietnamese authorities recently seized a Chinese ship they said had illegally entered Vietnamese waters carrying 100,000 liters of diesel fuel. Meanwhile, state media in Hanoi reported that the captain of the three-man vessel as saying the boat was supplying oil to Chinese fishing boats in the area.

The Vietnamese government’s statement comes just days after the country’s legislature swore in Prime Minister Nguyen Xuan Phuc, who has vowed to defend Vietnam’s sovereignty.

The disputed oil rig, towed by China National Offshore Oil and known as HYSY 981, was at the center of standoff between the countries in 2014 when China parked it near the Paracel islands that Vietnam claims as its exclusive economic zone. The incident sparked deadly riots in Vietnam.