A Navy destroyer sailed close to disputed South China Sea islands in a direct challenge to Chinese maritime claims over the strategic waterway.
U.S. and allied warships and aircraft have stepped up naval and air patrols to challenge China's claims to control about 90 percent of the South China Sea. The USS Wayne E. Meyer, a guided-missile destroyer, conducted a freedom of navigation operation in the South China Sea on Friday.
"This freedom of navigation operation (FONOP) upheld the rights, freedoms, and lawful uses of the sea," Cmdr. Reann Mommsen, a spokeswoman for the Pacific Fleet, said in a statement.
Mommsen did not disclose details of the location, or whether Chinese warships shadowed the Meyer and tried to order it out of the area, a practice followed during past encounters.
The Meyer conducted a similar passage in late August near Fiery Cross Reef and Mischief Reef in the Spratly Islands, located in the southern part of the sea.
China's military denounced the warship operation as "navigational hegemony."
In a statement, the Chinese military said the U.S. warship "trespassed" into Chinese waters without permission near the Xisha Islands, Beijing's name for the Paracel Islands. The Paracels are a group of islands in the northern part of the Southeast Asian sea that are claimed by China, Vietnam, and Taiwan.
"The U.S. side has been practicing 'navigational hegemony' in the South China Sea for a long time," Li Huamin, a spokesman for the PLA Southern Theater Command said in the statement. "Such actions have seriously undermined China's sovereign interests, and proven the U.S. side's complete lack of sincerity in maintaining global peace as well as regional security and stability."
China has built up military facilities on Woody Island in the Paracels over the past seven years. The Pentagon estimates China's island reclamation and subsequent militarization efforts involve some 3,200 acres of new islands.
On June 20, commercial satellite firm ImageSat International disclosed satellite images on Twitter revealing China's military had deployed at least four J-10 fighters to Woody Island in the Paracels. It is the first warplane deployment there since China deployed J-11 fighters in 2017.
Earlier warplane deployments on Woody Island have included sending H-6 nuclear-capable bombers for temporary deployment.
The Pentagon's latest annual report on the Chinese military said the deployment of advanced anti-aircraft and anti-ship missiles on disputed South China Sea islands violates a promise by Chinese president Xi Jinping. Xi told the United States in 2015 that China would not militarize disputed islands in the sea.
"The South China Sea plays an important role in security considerations across East Asia because Northeast Asia relies heavily on the flow of oil and commerce through South China Sea shipping lanes, including more than 80 percent of the crude oil to Japan, South Korea, and Taiwan," the report said.
"China claims sovereignty over the Spratly and Paracel Island groups and other land features within its self-proclaimed 'nine-dash line' – claims disputed in whole or part by Brunei, the Philippines, Malaysia, and Vietnam. Taiwan, which occupies Itu Aba Island in the Spratly Islands, makes the same territorial assertions as China."
The U.N. Permanent Court of Arbitration ruled against China in 2016, stating that Beijing's claims of historic rights over the South China Sea were invalid and are limited by the Law of the Sea Convention.
China did not take part in the arbitration and rejected the court's findings. However, the Pentagon report said "by the terms of the Convention, the ruling is binding on China."
Mommsen said all claimants to the Paracels require permission or advance notification before foreign military vessels conduct innocent passage near the islands.
"The unilateral imposition of any authorization or notification requirement for innocent passage is not permitted by international law, so the United States challenged these requirements," she said.
By conducting the passage without notifying any state or seeking permission, the United States "protested the unlawful restrictions imposed by China, Taiwan and Vietnam," Mommsen explained. "The United States demonstrated that innocent passage may not be subject to such restrictions."
In addition, the destroyer "contested China's claim to straight baselines enclosing the Paracel Islands," Mommsen said.
In a lengthy legal explanation for the operation Mommsen discussed China's drawing of baselines entirely around the Paracels.
"With these baselines, China has attempted to claim more internal waters, territorial sea, exclusive economic zone, and continental shelf than it is entitled under international law," she said.
The U.S. warship showed China that "these waters are beyond what China can lawfully claim as its internal waters or territorial seas and that China's claimed straight baselines around the Paracel Islands are inconsistent with international law," Mommsen said.
The spokeswoman insisted that all Navy freedom of navigation operations are carried out legally under international law and demonstrate that the United States will fly aircraft, sail ships, and otherwise conduct military operations wherever international law permits, regardless of excessive claims by states like China.
"The Freedom of Navigation Program's missions are conducted peacefully and without bias for or against any particular country," she said. "These missions are based in the rule of law and demonstrate our commitment to upholding the rights, freedoms, and lawful uses of the sea and airspace guaranteed to all nations."
While the Paracels are claimed by three nations, the dispute over them has mainly involved China and Vietnam.
In 1974, both states engaged in what is called the battle of the Paracel Islands. In the battle, Vietnamese forces attempted to force Chinese naval vessels out of the Paracels. As a result of the battle, China established de facto control over the islands.
In July, Vietnam called on China to remove a sea survey vessel and coast guard ships from Vanguard Bank in the Spratly Islands, the other major grouping of disputed islands.
That dispute followed the May 2014 confrontation between Hanoi and Beijing over the deployment of a Chinese oil platform near the Paracels.
Vietnam sent ships to stop the rig from drilling into the seabed and were met by Chinese escort ships. Both nations' ships were involved in ramming incidents.