MANILA, Philippines  >> The Philippines on Friday accused China of escalating the countries’ 10-day standoff in the disputed South China Sea by sending a third patrol vessel to a shoal where both sides claim sovereignty.

The standoff at the Scarborough Shoal, sparked April 10 when the Philippines accused Chinese fishermen of poaching in its territory, is being closely watched to see how far Beijing will go in its increasingly assertive stance on territorial claims in the region. The South China Sea is home to a myriad of competing claims, also involving Vietnam, Brunei, Malaysia and Taiwan.

The latest Chinese patrol vessel was dispatched after the Philippines refused to withdraw its coast guard ship from Scarborough Shoal, China’s state-run Xinhua news agency said.

Philippine Foreign Affairs spokesman Raul Hernandez told a news conference in Manila that China’s move was seen as an escalation of the standoff originally sparked when two Chinese maritime surveillance ships prevented a Philippine warship from arresting several Chinese fishermen. The fishermen slipped away from the shoal, angering Philippine officials.

The Philippines subsequently replaced the warship with a smaller coast guard vessel that was facing off with the two Chinese ships, with each side demanding the other pull out first.

Hernandez said that his government plans to ask China’s representatives why they violated an earlier agreement not to aggravate the situation.

"We understand that the world is watching, and the issue at hand has a wider implication on how China is asserting its territorial claims, which have no basis in international law," Hernandez said.

Foreign Secretary Alberto del Rosario, who is currently on a visit to the U.S., said earlier that the Philippines cannot compete with China militarily and was seeking a diplomatic solution.

Hernandez said the Philippines was ready to take the dispute to an international court despite China’s earlier rejection of that idea.

"It is the proper and competent forum to decide the issue," he said.

In Beijing, Foreign Ministry spokesman Liu Weimin said that the reason for the third ship was because the Philippines violated China’s jurisdiction and interfered with Chinese fishermen.

He said Beijing hoped the Philippine side would "work with us to ease tension" and that senior Philippine officials "won’t mislead the public any more."

The shoal, which lies in what the Philippines considers its 370-kilometer (230-mile) exclusive economic zone, is among numerous islands, reefs and coral outcrops in the South China Sea claimed by China, the Philippines and other nations for their potential oil and gas deposits, rich fishing grounds and proximity to busy commercial sea lanes.

About 100 Filipino demonstrators called on China to withdraw from the shoal in a third day of protests outside the Chinese Consulate in Manila.

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Associated Press writer Scott McDonald in Beijing contributed to this report.