The Philippines on Tuesday said it had successfully delivered supplies to marines aboard the BRP Sierra Madre, a dilapidated military outpost in the contested South China Sea, despite attempts by Chinese vessels to block the mission.

The National Task Force for the West Philippine Sea said in a statement that it successfully delivered supplies to the stranded landing ship on the Second Thomas Shoal in Manila’s exclusive economic zone, which China calls Renai Reef and also claims as its sovereign territory.

The mission was carried out despite attempts by the “China Coast Guard and Chinese Maritime Militia to block, harass, and interfere” with the supply mission, the task force said.

China’s maritime militia is hundreds of vessels strong and acts as an unofficial – and officially deniable – force that Beijing uses to push its territorial claims both in the South China Sea and beyond, according to the Philippines, the United States and Western marine security experts.

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Videos released Tuesday by the Philippine Coast Guard showed two Chinese vessels at close range of a Filipino ship, appearing to block its path to the BRP Sierra Madre.

It comes after China faced international backlash for firing a water cannon on a much smaller Philippine boat that was attempting to deliver supplies to the military outpost more than two weeks ago.

The World War II-era navy transport ship was intentionally grounded in 1999 by the Philippines to enforce the country’s claim to the area. The BRP Sierra Madre is mostly a rusted wreckage and is manned by Filipino marines stationed on rotation.

China’s Coast Guard responded saying it firmly opposed the Philippines for “taking advantage” of the opportunity to resupply “illegal construction materials used for large-scale reinforcement” at the disputed shoal, its spokesman Liu Dejun said.

Liu said two Philippine supply vessels and two marine police vessels entered the waters “without the permission of the Chinese government.”

The South China Sea has long been a source of tension between Manila and Beijing.

Beijing claims “indisputable sovereignty” over almost all of the 1.3 million square mile South China Sea, as well as most of the islands within it, even those hundreds of miles from the Chinese mainland.

The Philippines, Malaysia, Brunei, Vietnam and Taiwan also lay claim to various atolls, sandbars and islands of the sprawling South China Sea.

Manila’s territorial claims are backed by the international Permanent Court of Arbitration in the Hague, which ruled in 2016 that China has no legal basis to claim historic rights to the bulk of the South China Sea.

Beijing has ignored the ruling and insists that the Philippines had promised to remove the vessel. Philippine President Ferdinand Marcos Jr. said that his government has never promised such a move.

“And let me go further, if there does exist such an agreement, I rescind that agreement now,” Marcos Jr. said in a video statement on August 9.

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