China accused the Philippines of violating its sovereignty on two separate occasions over the weekend after its neighbor to the southeast undertook supply missions to South China Sea features claimed by both countries.

Beijing also said one of the Philippine ships had rammed one of its coast guard vessels near the disputed Second Thomas Shoal.

The incidents took place at Scarborough Shoal and Second Thomas Shoal, two of the most hotly contested areas in the region. China asserts historical rights to upward of 80 percent of the trade-rich sea as its territory, while the Philippines claims its ships have a right to operate within its exclusive economic zone, as defined in the UN Convention on the Law of the Sea (UNCLOS).

Second Thomas Shoal

Philippine supply ships and their two coast guard escorts on Sunday “intruded into adjacent waters of Ren’ai Jiao [Second Thomas Shoal] in China’s Nansha Qundao [Spratly Islands] in an attempt to send construction materials to the illegally grounded warship at the reef,” Chinese Foreign Ministry spokesperson Mao Ning said at Monday’s regular press conference.

The warship in question was the BRP Sierra Madre, a former U.S. tank landing ship the Southeast Asian country grounded in 1999 to stake its claim at Second Thomas Shoal, which the Philippines calls Ayungin Shoal. Manila maintains a small group of marines there, and its missions to resupply them have become lightning rods for Chinese maritime forces seeking to block them.

Citing “the long course of history,” the spokesperson said an international tribunal’s ruling in favor of the Philippines was “illegal, null and void” and said the Philippines had broken a promise not to deliver construction supplies for the repair of the dilapidated warship.

Footage captured by members of the supply mission shows Chinese coast guard ships deploying their water cannons against the Philippine boats. Video shows one of the supply boats bumping against the blocking Chinese ship before continuing on its mission. Philippine government photos uploaded to social media allegedly show another supply boat being towed back to port after a water cannon damaged its engine.

In a statement published Sunday, the Chinese coast guard said it had taken restrictive measures against the disabled ship—the Kalayaan—for allegedly ferrying construction supplies but granted “temporary special arrangements” for the other supply ship, the Yunaza May 1, which was allegedly carrying food and other necessities.

Chinese state-backed media outlet the Global Times cited anonymous analysts who said the U.S. treaty ally and Western media were exaggerating how aggressive deploying water cannons is. In fact, their use “reflects China’s restraint in dealing with the Philippine provocations in a move to avoid a potential escalation,” the outlet said.

Scarborough Shoal

Three ships from the Philippine government’s fisheries bureau “intruded into the waters adjacent to China’s Scarborough Shoal” on Saturday despite multiple warnings, according to a Chinese coast guard statement published Sunday.

The coast guard ships reacted in a “professional, standard, legitimate, and legal” manner, the statement said, urging the Philippines to adhere to international norms and law.

The Philippines published video footage over the weekend showing the Chinese coast guard using their water cannons against the fisheries ships on their way to deliver provisions to waiting Philippine fishermen. Manila condemned China for interfering with what it called a humanitarian mission and for scattering the fishermen.

The Philippines also accused China’s paramilitary maritime militia, whose boats were on the scene, of inflicting “severe temporary discomfort” on Filipino crew members with unspecified “acoustic devices.”

“For some time now, the Philippines has frequently sent ships and planes to invade the waters and airspace adjacent to China’s Nansha Islands and Huangyan Island,” Chinese embassy to the U.S. spokesperson Liu Pengyu told Newsweek Friday. He added that this was seriously impacting stability in the South China Sea and called on the Philippines to “return to the right track” by engaging in negotiations and consultation to settle maritime disputes.

Entrenched positions

China hopes this non-military pressure will convince the Philippines and fellow South China Sea claimants Vietnam, Brunei, and Malaysia that resistance is futile and they should acknowledge China’s claimed historic rights, Greg Poling, director of the Southeast Asia Program at the Center for Strategic and International Studies think tank previously told Newsweek.

Earlier this month, Chinese President Xi Jinping declared a need to “resolutely defend China‘s territorial sovereignty and maritime rights and interests.”

Xi’s Philippine counterpart Ferdinand Marcos Jr. on Sunday vowed the Philippines would likewise continue to press its territorial claims.

“The aggression and provocations perpetrated by the China Coast Guard and their Chinese Maritime Militia against our vessels and personnel over the weekend have only further steeled our determination to defend and protect our nation’s sovereignty, sovereign rights, and jurisdiction in the West Philippine Sea,” Marcos Jr. said.

The West Philippine Sea is Manila’s name for the portions of the South China Sea that lie within the country’s economic exclusive zone.

A number of countries joined the U.S. in issuing statements against China’s operations over the weekend, criticizing its coast guard’s acts as unsafe and expressing support for the 1982 UNCLOS.