HANOI, Vietnam - Vietnam protested to China on Thursday after what it described as a "premeditated" attack on an exploration ship in its waters, raising tensions between the Communist neighbors.
The latest incident comes against a backdrop of increased anti-Chinese sentiment in the Southeast Asian nation, where hundreds of people staged a rare protest Sunday over the activities of Chinese ships in disputed waters.
With ties between Beijing and Hanoi at their lowest in years owing to territorial spats over potentially oil-rich waters, Prime Minister Nguyen Tan Dung vowed to protect Vietnam's "incontestable" sovereignty.
Hanoi said a Chinese fishing boat "intentionally rammed" the exploration cables of a vessel, chartered by state energy giant PetroVietnam, conducting a seismic survey inside its 200 nautical mile exclusive economic zone Thursday.
The incident was "premeditated and carefully calculated" as China aims to bring an undisputed area into the territorial row, foreign ministry spokeswoman Nguyen Phuong Nga told reporters.
"This is unacceptable to Vietnam," she said, adding that the foreign ministry had met Chinese embassy officials Thursday afternoon "to express our opposition to such acts."
Two Chinese fishing enforcement vessels and other fishing boats arrived to assist the Chinese boat, Nga said, adding that the collision affected the Vietnamese ship's ability to operate normally.
She said the area in question is completely under Vietnamese sovereignty according to the 1982 United Nations Convention on the Law of the Sea.
It comes just two weeks after three Chinese marine surveillance vessels severed the exploration cables of the Binh Minh 2, another Vietnamese oil survey ship inside the 200 nautical mile zone, according to Hanoi.
Vietnam said it has since deployed eight ships to "escort" the Binh Minh 2 -- without saying what kind of vessels -- a move which analysts say raises the stakes in the dispute.
After the May 26 incident China said Vietnamese vessels were operating "illegally" and urged the country to "refrain from creating trouble."
Dung, communist Vietnam's most powerful figure, made his first public comments on the latest dispute in an article in the Thanh Nien daily published Thursday, indicating how seriously the government views the situation.
He reaffirmed "the incontestable maritime sovereignty of Vietnam towards the two archipelagos, the Paracels and Spratlys," which the people and army have "the strongest determination" to protect.
Beijing says it is committed to peace in the South China Sea, but its more assertive maritime posture has caused concern among regional nations.
Tensions have also risen this year between China and the Philippines, another claimant to the Spratlys, where Malaysia, Brunei and Taiwan also say they have a stake.
US Defense Secretary Robert Gates warned last weekend that clashes may erupt in the South China Sea unless nations with conflicting territorial claims adopt a mechanism to settle disputes peacefully.
Hundreds of people held a peaceful anti-China protest outside Beijing's embassy in Hanoi on Sunday, the largest action of its kind since 2007. Protests are rare in authoritarian Vietnam.
"I think the pressure is on China to stop these acts," said Australia-based Vietnam analyst Carl Thayer.
Tensions have also spread to the Internet.
In the past few days a number of Vietnamese websites have been hacked including one connected with the foreign ministry, with information in Chinese and images of the Chinese flag left behind, Nga said.