Online Desk: The Chinese military said that an American naval ship had “illegally intruded” on Monday into waters near the Second Thomas Shoal, the site of a hot territorial dispute between China and the Philippines in the South China Sea.

A Chinese naval force was mobilized to track the USS Gabrielle Giffords during the operation, according to a statement from the People’s Liberation Army Southern Theater. The U.S. Navy’s 7th Fleet said the ship “was conducting routine operations in international waters … consistent with international law.”

Chinese and Philippine naval and coast guard ships have confronted each other repeatedly around the shoal in the Spratly Islands in recent months as China tries to prevent the Philippines from resupplying and repairing a rusting warship that it intentionally ran aground in 1999 to serve as a military outpost.

Dwarfed by China’s military might, the Philippines has sought America’s help in its multiple territorial disputes with China in the South China Sea. President Ferdinand Marcos Jr. agreed to an expansion of the U.S. military presence in the country early this year and launched joint sea and air patrols with the United States late last month.

China accuses the U.S. of meddling in waters far from its shores and renewed its charge that America is the one raising regional tensions following the sailing of the USS Giffords near Second Thomas Shoal. The ship is a littoral combat ship designed to operate in coastal areas.

“The U.S. deliberately disrupted the situation in the South China Sea, seriously violated China’s sovereignty and security, seriously undermined regional peace and stability, and seriously violated international law and basic norms governing international relations, fully demonstrating that the U.S. is the biggest threat to peace and stability in the South China Sea,” the statement from the Chinese military’s Southern Theater said.

China has staked claim to virtually all of the reefs and other outcroppings in the South China Sea, building some into islands with runways that could be used by the military. Vietnam, Malaysia, Taiwan and Brunei also say they are the rightful owners of territory in the same waters in a complex web of overlapping claims.

The U.S. has long been the major military power patrolling the South China Sea, an important shipping lane and fishing grounds, operating out of bases in the Pacific. China’s emergence as a military power and its ambitions to be a regional and global power are challenging American long-standing dominance.

A statement from the U.S. Navy’s 7th Fleet, based in Japan, said its operations in the South China Sea demonstrate a commitment “to upholding a free and open Indo-Pacific region where all nations, large and small, are secure in their sovereignty, can resolve disputes without coercion, and have the freedom to navigate and fly consistent with international laws, rules and norms.”

The Philippine coast guard said Sunday that it had sent two ships to Whitsun Reef, another disputed territory in the Spratly Islands, to challenge and document what it estimated to be more than 135 Chinese vessels massing in the area. The Philippines called them a maritime militia and said their presence is illegal. The vessels did not respond to radio challenges, the coast guard said.

China, as in similar incidents in the past, said the reef belongs to China and that the nearby waters are an important operating area and shelter for Chinese fishing boats.

“It is reasonable and lawful for Chinese fishing boats to operate and take shelter in the waters,” Foreign Ministry spokesperson Wang Wenbin said. “The Philippine side should not make irresponsible remarks about that.”