Vietnam demanded Friday that China remove an oil exploration rig from a sea area where the countries are still negotiating a delineation of control and stop complicating the situation with unilateral action.

The oil rig 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.

Foreign Minster spokesman Le Hai Binh said China had moved the oil rig into an area in the Gulf of Tonkin where the countries are conducting delineation.

"Vietnam resolutely opposes and demands that China abandon drilling plans and immediately withdraw the Hai Duong 981 oil rig from this area, and that it not take additional unilateral actions that further complicate the situation" in the South China Sea, he said in a statement, referring to the oil rig by its Vietnamese name.

He said Vietnam had lodged a protest with the Chinese Embassy in Hanoi.

Binh also said that the start of operations of a lighthouse on one of the seven artificial islands China had built in the South China Sea was "illegal and invalid."

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