The U.S. Navy sailed alongside a group of disputed islands in the South China Sea on Sunday in the latest sign of escalating tensions with China.

The USS Decatur guided-missile destroyer sailed within 12 nautical miles of two Spratly Island reefs on “freedom of navigation operations” on Sunday, two American officials told CNN. China has built military installations on the strategically located Spratly archipelago, parts of which are also claimed by the Philippines, Vietnam, Malaysia and Taiwan.

The “freedom of navigation missions” are designed to challenge “excessive maritime claims,” an American military official told CNN.

“The United States will fly, sail and operate wherever international law allows,” the official added.

China claims dominion over a number of island groups in the heavily contested South China Sea, and has recently ramped-up development of artificial islands and military facilities despite international condemnation.

In May, the new U.S. Pacific Command chief warned that “China is now capable of controlling the South China Sea in all scenarios short of war.”

Read more: China Has Begun New Work in the Disputed South China Sea

But the U.S. has continued to challenge China’s policing of those waters. In May, the U.S. Navy sailed two ships near the Paracel Islands, another contested island group, prompting an outraged response from China’s Ministry of Defense. Earlier this week, the U.S. also flew two B-52 bombers over China-claimed territory.

The sail-by on Sunday also comes amid heightened tensions between Washington and Beijing over trade and diplomatic issues. Last week, new tariffs targeting $200 billion of Chinese goods came into effect, the latest salvo in President Donald Trump’s ongoing trade war with China. Trump also accused China of interfering with the upcoming U.S. 2018 midterm elections at the U.N. Security Council.

Read more: Aboard the USS Carl Vinson in the South China Sea

Those tensions appear to be spilling over into military cooperation. China canceled a high-profile Beijing security summit later this month, and prevented a U.S. Navy ship from docking in Hong Kong, the New York Times reports.

Last week, the Trump administration also announced a $330 million weapons sale to Taiwan, and imposed sanctions on a Chinese defense contractor that bought Russian-made weapons.

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Write to Eli Meixler at eli.meixler@time.com.