BANGKOK—Tensions in the potentially resource-rich South China Sea flared as Vietnam accused China of sabotaging a seismic survey boat while China warned its neighbors to stop looking for oil in the disputed territory without its permission.
Beijing's efforts to extend the reach and influence of its military, alongside its hunger for natural resources, have contributed to mounting worries in recent months over the stability of the South China Sea.
The conflict has escalated into a series of clashes between Vietnamese exploration craft and Chinese patrol boats and a worsening war of words with the Philippines.
The territorial disputes were a focus of a regional security conference in Singapore on Saturday, where Defense Secretary Robert Gates said the U.S. was committed to defending its Southeast Asian allies. Mr. Gates predicted more clashes could occur unless rival claimants find a way to peacefully settle their disputes.
Yet Secretary of State Hillary Clinton's move to offer Washington's assistance in facilitating multiparty talks over the waters while visiting Vietnam last year infuriated China.
In the latest incident, Vietnam's Foreign Ministry on Thursday said a Chinese fishing boat supported by two Chinese naval patrol craft cut a cable being used by a seismic survey craft operated by state-run energy company PetroVietnam.
Ministry spokeswoman Nguyen Phuong Nga said the Chinese boat's actions were "completely premeditated" and "seriously violated Vietnam's sovereign rights."
China's ambassador to the Philippines, Liu Jianchao, denied any wrongdoing in the area while also urging South China Sea claimants to stop drilling for oil and gas.
Security analysts say the incident reflects a pattern of Chinese muscle-flexing in the disputed waters, which are claimed in whole or in part by Vietnam, the Philippines, Taiwan, Brunei and Malaysia in addition to China, which considers the entire South China Sea as its sovereign territory.
The trigger for the worsening disputes is largely economic, says Carlyle Thayer, a professor at Australian Defence Force Academy at the University of New South Wales. The semi-submerged islands and reefs of the South China Sea—especially the Spratly Islands and the Paracels—are believed to lie atop significant reserves of oil and natural gas. Vietnam and the Philippines are already tapping some fields in the region.
China "seeks to control these resources because they are abundant and closer to home than oil from the Middle East," Mr. Thayer said.
The Chinese navy can also protect the sea routes over which South China Sea oil must be carried, he said. "The South China Sea forms one part of a larger effort by China to secure energy supplies around the world in order to fuel its high economic growth rates," he said.
Vietnamese Prime Minister Nguyen Tan Dung, in his first public comments since Vietnam's dispute with China worsened, on Wednesday described Vietnam's claims to the South China Sea as "incontestable," a sign of Hanoi's willingness to stand up to China.
China has said it wants to preserve peace in the region and negotiate sea disputes. But it also has argued neighboring countries are undermining its interests in the South China Sea.
"We're calling on other parties to stop searching for the possibility of exploiting resources in these areas where China has its claims," said Mr. Liu, the ambassador, in Manila. "We will never use force unless attacked," he added.
Two weeks ago, Vietnam accused a Chinese patrol craft of cutting the cables on another survey boat. Like the incident on Thursday, it occurred within 200 nautical miles of Vietnam's coast, which Vietnam regards as its own exclusive economic zone as provided under international law.
In a similar incident in March, the Philippine military said two Chinese boats disrupted a Philippine oil exploration boat's activities near the Reed Bank, west of the Philippines' Palawan province.
The Philippine government also accuses China's navy of firing on Filipino fisherman at Jackson Atoll, which is near the Philippines and claimed by that country, in late February.
The Philippines has filed a series of complaints with the United Nations about China's alleged behavior in the South China Sea.
Security analysts say a concerted effort among the smaller claimant countries—especially Vietnam and the Philippines, with U.S. backing—to internationalize a settlement over the South China Sea might be goading China into increasingly belligerent responses.
Vietnam has pressed for the 10-member Association of Southeast Asian Nations to play a central role in resolving tensions in the area. The Philippines, an Asean member that had spent several years trying to firm up political and economic alliances with China, has also begun pushing for multiparty talks in recent months.
In the meantime, stresses and strains in the region continue to deepen, especially in Vietnam. Some 200 Vietnamese demonstrators protested against China's expanding influence over the sea on Sunday in a rare public display against a fellow Communist nation—an event which some analysts say must have involved a degree of support from the Vietnamese authorities, given its tight control over public dissent.
Hanoi previously has offered its navy base at Cam Ranh Bay as a repair and refueling stop for foreign navies operating in the region—a move that analysts expect could prompt a flood of port calls from vessels from countries such as Australia, Russia, India and the U.S.
Vietnam is also buying six Kilo-class submarines from Russia to help expand its reach in the South China Sea and also help counteract China's growing naval power.
Write to James Hookway at email@example.com