HANOI – Vietnam has demanded that China remove an oil survey vessel and its escorts from the Southeast Asian country’s exclusive economic zone, amid a month-long standoff in waters seen as a potential global flashpoint as the United States challenges Beijing’s maritime claims.

Reuters first reported on Tuesday that the Haiyang Dizhi 8, conducted by the China Geological Survey, had returned to the area escorted by at least two Chinese coast guard vessels.

“Vietnam has made contact with China to protest its repeated violations and demanded that China withdraw the vessel group from Vietnamese waters,” Vietnam’s Foreign Ministry spokeswoman Le Thi Thu Hang said in a statement.

At least five Chinese coast guard ships were escorting the survey vessel, and at least two Vietnamese navy vessels were following the group of Chinese ships as of late Friday, according to data from Marine Traffic, a website that tracks vessel movements.

The Haiyang Dizhi 8 first entered the zone under Chinese coast guard escort in July and appeared to conduct a seismic survey of waters there.

The latest impasse has fuelled anti-Chinese sentiment in Vietnam, where previous tension between Beijing and Hanoi over the disputed waters has triggered protests.

Last week, police broke up a brief protest outside China’s embassy in Hanoi against the operations of the survey vessel and its escorts.

U.S. Secretary of State Mike Pompeo has criticised Chinese “coercion” in the disputed South China Sea, while Beijing’s top diplomat, Wang Yi, said last month that maritime problems involving Vietnam should not interfere with two-way ties.

After the Haiyang Dizhi 8 left Vietnam’s EEZ on Aug. 7, the survey ship docked at Fiery Cross Reef, a man-made island controlled by China and built on a disputed South China Sea reef claimed by Vietnam and the Philippines.

Hang said in her Friday statement that Vietnam is determined to protect its legitimate and legal interests in the area.

“Vietnamese authorities continue to take measures to exercise sovereignty, sovereign rights and jurisdiction in accordance with Vietnamese law and international law,” Hang said.