The monthlong standoff between China and the Philippines over a South China Sea shoal is snowballing with hints of economic retaliation and sharpening public opinion that are narrowing the space for a negotiated settlement.

Beijing is suspending some tourism to the Philippines and stiffening inspections on Philippine fruit such as bananas, of which China is the single largest buyer. That follows Beijing's summoning of Manila's charge d'affairs three times, while retired and serving military officers have called for a limited military operation to shore up China's credibility on the matter — a potentially explosive move that could trigger the 1951 U.S.-Philippine Mutual Defense Treaty.

"The Chinese Foreign Ministry has made it clear China is prepared for any escalation of the situation by the Philippines. It goes without saying what this means," the military's official Jiefangjun Bao newspaper said in an editorial.

The Philippines has registered its own diplomatic protests, cautioning foreign governments over a perceived Chinese threat to freedom of navigation and preparing to bring the dispute to international arbitration. The Philippines is also seeking to back up its territorial claims with new warships, fighters jets and radars from the United States.

Actions on both sides are shrinking the room for political maneuverability, but they are exacerbated by perceptions that Washington is backing what Chinese see as deliberate provocations by the Philippines, said Jonathan Holslag, a research fellow at the Institute for Contemporary China Studies at the University of Brussels.

"China can't give in, since that would be the same as backing down to American bullying," Holslag said.

The two nations are among six claimants to waters and island groups in the South China Sea, home to heavily traveled maritime lanes, rich fishing grounds and a potential wealth of mineral resources.

The latest confrontation began April 10 when the Philippine navy accused Chinese boats of fishing illegally around Scarborough Shoal, which Manila claims as part of its exclusive economic zone, but which Beijing insists has been Chinese for centuries.

A civic group in the Philippines has called for protests Friday, prompting China to warn its citizens in the Philippines.

Beijing's moves on tourism and fruit imports are a variation of unacknowledged economic pressure employed in past international disputes.

China International Travel Service, one of the country's largest, said it was suspending trips from Thursday based on safety considerations. Nationwide online agency Ctrip.com has also suspended trips, an agent said, citing "anti-China sentiments in that country right now." She said the company acted on its own without official orders.

The Shanghai Tourism Bureau had also ordered a suspension, according to staff with the Yiyou and Guojikuaixian travel agencies in the eastern financial hub.

None of the agents would give their names because of the sensitivity of the matter. Calls to China's national tourism administration rang unanswered Thursday. Chinese tourists also make up about 9 percent of total arrivals to the Philippines, according to the Philippines Department of Tourism.


Associated Press writers Jim Gomez and Hrvoje Hranjski in Manila, Philippines, contributed to this report.