In a demonstration of how exploration of oil and gas is a crucial aspect of the South China Sea territorial disputes, American and Philippine naval exercises this month will include one that involves retaking a hijacked oil rig, according to the Philippine military. The current naval standoff began Sunday when Philippine surveillance aircraft spotted eight Chinese fishing boats near Scarborough Shoal, an outcropping of rocks 124 nautical miles west of Luzon Island in the Philippines. The shoal, which is called Panatag in the Philippines and Huangyan in China, is claimed by both countries.

The Philippine Navy sent the Gregorio del Pilar, a 378-foot patrol frigate that was formerly an American Coast Guard cutter. The ship arrived early Tuesday and found the boats anchored inside the horseshoe-shaped shoal, according to Vice Adm. Alexander P. Pama.

“At about 7:20 in the morning, the boarding team started to conduct a board, search and seizure on the first Chinese fishing vessel and found large amounts of corals, sizable quantities of giant clams and live sharks in its compartments,” Admiral Pama told reporters on Wednesday, adding that the other Chinese boats carried similar sea resources that he said were illegal to harvest.

On Tuesday afternoon, two Chinese surveillance ships, identified by Philippine officials as Zhonggou Haijian 75 and Zhonggou Haijian 84, took positions at the mouth of the lagoon within the shoal, blocking the Philippine Navy vessel’s access to the fishing boats inside.

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One of the Chinese ships radioed the Philippine ship and said that the area was Chinese territory and that the Philippine Navy should withdraw. The Philippine captain responded that the shoal was his country’s territory. As of late Wednesday, the vessels remained in position.

In its statement, the Chinese Embassy said the fishing boats were in the lagoon seeking shelter from a storm when “a Philippine Naval gunboat blocked the entrance of the lagoon, and sent 12 Philippine soldiers, 6 of which armed, into the lagoon and harassed the Chinese fishermen.”

It went on to say that the embassy had contacted the Philippine government and “reiterated China’s sovereignty over Huangyan Island, urged the Philippine side to stop immediately their illegal activities and leave this area.”

Scarborough Shoal, which sits amid rich fishing grounds, has been a point of contention for more than a decade between China and the Philippines. Fishermen from both countries have had previous confrontations with opposing naval vessels.

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The Philippines claims the area as part of its 200-mile exclusive economic zone, while China says that the area was mapped as Chinese territory as early as the 13th century. The shoal lies north of the Spratly Islands, which are also claimed by China, the Philippines and other Southeast Asian nations.

In Beijing last week, a Foreign Ministry spokesman reiterated that China had “indisputable sovereignty” over the Spratly Islands and their adjacent waters, and “resolutely” opposed actions by other countries that “damage China’s sovereignty.”

In an article published online this week, a Chinese Army officer accused the Philippines of trying to use American power to intimidate China. The officer, Maj. Gen. Luo Yuan, warned that China might reconsider its planned $50 billion investments in the Philippines.

Last week, at a summit meeting of Southeast Asian leaders, China strongly opposed an effort by the Philippines and Vietnam to draft a regional code of conduct to resolve the territorial disagreements.