Hanoi last month accused Chinese surveillance vessels of cutting the exploration cables of an oil surveyship inside the area.
上个月，河内指责在该海域中国侦察艇切断了其一艘石油探测船的电缆。
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Earlier this year, five Chinese vessels were involved in a stand-off with a surveyship from the US navy off China's Hainan Island.
今年早些时候，五艘中国舰艇在中国的海南岛与一艘美国海军的侦察船相对峙。
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On Thursday, Vietnam alleged a similar incident in the zone, saying a Chinese fishing boat rammed the cables of another oil surveyship in a "premeditated" attack.