The Philippine Foreign Ministry said on Wednesday that US spy planes are providing crucial intelligence about the activities of Chinese vessels in the South China Sea.

"I think it's of significant importance for us," Philippine Foreign Secretary Albert del Rosario told reporters, when asked about the value of the information gathered by US military surveillance aircraft.

Observers said it shows that Manila is seeking further support from Washington on the South China Sea issue, though the United States does not want to sacrifice its ties with Beijing for the sake of furthering Manila's interests.

"The Philippines is continually seeking more international support, especially from the US, in order to better bargain on territorial issues with China," said Chen Qinghong, a researcher on Philippine studies at the China Institutes of Contemporary International Relations.

"Through playing up its close ties with the US, Manila's ultimate purpose is to make the US, its close ally, become directly involved in the issue," said Ren Yuanzhe, a researcher on Asia-Pacific studies with China Foreign Affairs University.

Beijing and Manila have held negotiations on territorial disputes concerning some islands in the South China Sea and have reached agreements in some areas. As approved by the two governments, China National Offshore Oil Corp and Philippine National Oil Co signed an agreement for joint marine seismic explorations in certain areas of the South China Sea.

Vietnam later joined the agreement, and the three parties have since carried out joint seismic operations in the area.

However, tensions have risen in recent years with the Philippines changing its attitude toward the South China Sea issue, illegally occupying some of the islands and reefs belonging to China's Nansha Islands.

The seizure of these territories is the direct cause of the current South China Sea dispute between the two countries, Foreign Ministry spokeswoman Hua Chunying said this month.

The Philippines has repeatedly called on the US for help in opposing China on the issue. While the US insists it will not take sides in the South China Sea territorial dispute, it has helped to upgrade the Philippines' military capabilities.

"Through helping the Philippines to strengthen its military power, the US wants to improve Manila's capability to resist China, and it is in this way that US shows its support to Manila," Chen said.

"Small-scale conflicts in the East Asia region are consistent with Washington's interests here, because they can help Washington to better implement its Asia-rebalancing strategy and for this reason it will not help eliminate those problems in the region," Ren said.

"But it is only Manila's own wishful thinking to drag Washington directly into the South China Sea territorial disputes because Washington knows it is not worthwhile to harm ties with Beijing for the sake of safeguarding Manila's interests," he added.

Zhang Fan and AFP contributed to this story.

zhouwa@chinadaily.com.cn