The Philippines deployed Monday resupply vessels to Second Thomas Shoal, locally known as Ayungin Shoal, a week after three Chinese coast guard vessels blocked and used water cannon on Philippine resupply boats in the area.

"The resupply ships left this morning Oyster Bay in Palawan and will reach (BRP) Sierra Madre tomorrow (Tuesday) morning," Defense Secretary Delfin Lorenzana told reporters.

• On Board the BRP Sierra Madre

He said he had received assurance from Chinese Ambassador Huang Xilian that the resupply mission will not be impeded. "Pero pakiusap nila
walang escort (But they asked that there will be no escort)," he said.

He added the Philippine military will remain in constant communication with the crew to monitor the mission and will deploy a Navy plane in the vicinity when the resupply ships are in Ayungin.

The Philippines on Thursday condemned "in strongest terms" the actions of three Chinese coast guard vessels that it said blocked and used water cannon on resupply boats headed towards a Philippine-occupied atoll in the South China Sea.

• DFA: Chinese Coast Guard vessels blocked PH supply boats in Ayungin Shoal

Foreign Secretary Teodoro Locsin said no one was hurt during Tuesday's incident at the Second Thomas Shoal but the Philippine boats, which were transporting food to military personnel based there, had to abort their mission.

"China has no law enforcement rights in and around these areas. They must take heed and back off," Locsin said in a statement, reminding China that a public vessel is covered by a Philippines-United States Mutual Defense Treaty.

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In response, Beijing claimed that the Filipino boats blocked and bombarded with water by Chinese coast guard vessels on Nov. 16 “trespassed” in Chinese waters in the West Philippine Sea.

In a press conference in Beijing, Chinese Foreign Ministry spokesperson Zhao Lijian claimed that the Chinese coast guard vessels only “performed official duties in accordance with law” and upheld what he said was “China's territorial sovereignty and maritime order.”

“Chinese coast guard vessels performed official duties in accordance with law and upheld China's territorial sovereignty and maritime order.

For its part, the United States accused China of an escalation against the Philippines and warned that an armed attack would invite a US response after an incident in disputed waters.

"The United States stands with our ally, the Philippines, in the face of this escalation that directly threatens regional peace and stability," State Department spokesman Ned Price said in Abuja, where Secretary of State Antony Blinken was travelling.

He warned that any "armed attack on Philippine public vessels" would invoke the 1951 US-Philippines treaty in which Washington is obliged to defend its ally.

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The Second Thomas Shoal, 105 nautical miles (195 km) off Palawan, is within the Philippines' exclusive economic zone and a small contingent of military have occupied it since 1999 having intentionally grounded a navy ship on the reef.

China regards the shoal as its territory as it falls within the "nine-dash line" that it uses on maps denoting its claim to almost the entire South China Sea. A 2016 international arbitration ruling, however, said the Chinese line had no legal basis.

Before the incident, National Security Adviser Hermogenes Esperon said authorities had noticed an unusual presence of Chinese maritime militia near the atoll and Philippine-occupied Thitu island. China has denied operating a militia.