By Manuel Mogato
MANILA (Reuters) - The Philippines air-dropped food and water to soldiers posted on a grounded transport ship on a disputed South China Sea shoal, after China blocked two supply ships from reaching the troops, a senior navy official said on Wednesday.
Chinese ships patrolling waters around Second Thomas Shoal, known in China as the Ren'ai reef, on Sunday ordered the Philippine ships carrying construction materials to leave the area.
Beijing claims Manila is trying to start construction on the disputed reef after it ran aground an old transport ship in 1999 to mark its territory and stationed marines on the ship. Manila claims the Shoal is part of the Philippine's continental shelf.
"We only intend to improve the conditions there, we have no plans to expand or build permanent structures on the shoal," said a Philippines navy official, who declined to be identified because he was not authorized to speak to the press.
"On Monday, we sent a navy Islander plane to drop food and water, but it will only last a few days. We really have to send back the civilian boats. Since last year, we've been resupplying our troops using civilian ships to avoid confrontation and this was the first time China blocked them."
On Tuesday, Manila summoned the second highest Chinese embassy official to hand over a strong-worded protest, calling the blockade "a clear and urgent threat to the rights and interests of the Philippines".
Chinese foreign ministry spokesman Qin Gang said China had called in Philippine diplomats in Beijing to lodge a protest in response.
"The Philippines' motive in trying to illegally occupy Ren'ai reef and create incidents in the South China Sea is abundantly clear. China calls on the Philippines to stop all its provocative actions," he added.
The Second Thomas Shoal, a strategic gateway to Reed Bank, believed to be rich in oil and natural gas, is one of several possible maritime flashpoints that could prompt the United States to intervene in defense of Asian allies troubled by increasingly assertive Chinese maritime claims.
WASHINGTON CALLS BLOCKADE "PROVOCATIVE"
On Wednesday, Washington said it was troubled by China's blockage of the Philippines ships, calling it "a provocative move that raises tensions."
"Pending resolution of competing claims in the South China Sea, there should be no interference with the efforts of claimants to maintain the status quo," U.S. State Department spokeswoman Jen Psaki said in a statement. She added that "freedom of navigation" in the area "must be maintained."
China has objected to efforts by Manila to challenge its territorial claims under the Law of the Sea at the Permanent Court of Arbitration at The Hague.
Ernest Bower of the Center for Strategic and International Studies think tank said new pressure on Manila could be due to China's perception that the United States has shown weakness in dealing with crises in Syria and Ukraine and will be similarly lacking in resolve in Asia - in spite of its declared policy "pivot" to the region.
It also reflected Chinese concerns about negotiations expected to bring about broader access for U.S. troops to the Philippines, he said.
"The Chinese see a very unhappy situation in the Philippines - that one of their smaller neighbors is taking them to court and working with the Americans for expanded military access," Bower said. "It does not fit with the Chinese script of where they want to be in terms of the South China Sea and their sovereign claims."
Bower said such incidents raised the risk that a small clash could escalate and it was important for the United States to make its commitment to the region clear ahead of a planned visit to Asia, including the Philippines, by President Barack Obama next month.
"The Chinese look at the situation in Syria and Ukraine and they look at the so-called Asia pivot and they don't think there is any political foundation that has been built that would support American action in Asia if push came to shove," he said.
Beijing's claim over islands, reefs and atolls that form the Spratlys, a group of 250 uninhabitable islets spread over 165,000 square miles, has set it directly against U.S. allies Vietnam and the Philippines, while Brunei, Malaysia and Taiwan also lay claim to parts of the South China Sea. China also has competing territorial claims further north with Japan, a major U.S. ally in Asia.
The South China Sea provides 10 percent of the global fish catch, carries $5 trillion in ship borne trade a year and its seabed is believed to be rich with energy reserves.
(Reporting by Manuel Mogato; Additional reporting by Ben Blanchard in Beijing and David Brunnstrom in Washington; Editing by Michael Perry and Sofina Mirza-Reid)