WASHINGTON, DC – The U.S. Navy conducted its second freedom of navigation operations in the South China Sea this week in a challenge to China’s disputed claim to islands there.

The USS Stethem, a guided missile destroyer, sailed within 12 nautical miles of Triton Island, part of the Paracel Islands in the South China Sea, a U.S. official told Reuters.

The operation angered China, whose foreign affairs ministry called it an unauthorized entry into China’s territorial waters.

“China strongly urges the U.S. side to immediately stop this kind of provocative action which seriously violates China’s sovereignty and puts at risk China’s security,” Ministry spokesman Lu Kang said, according to Reuters.

China’s Defense Ministry said the operation “seriously damages strategic trust” between the U.S. and China.

International law defines a nation’s territorial waters to be within 12 nautical miles of a country’s shores. China has claimed ownership over a string of islands and land features in the South China Sea disputed by Taiwan and Vietnam, as well as Malaysia, Brunei, and the Philippines.

U.S. policy is not to take sides in the territorial disputes, but to urge parties to resolve them peacefully through an international arbitration mechanism and to guarantee international passage through the waters by conducting such “freedom of navigation operations,” or FONOPs.

It was the second FONOP conducted under President Trump. The first occurred in late May when the destroyer USS Dewey sailed within 12 nautical miles of Mischief Reef in the South China Sea.

The Obama administration prohibited the U.S. Navy from conducting any FONOPs between 2012 and 2015 out of concern for angering China.

The FONOP comes as the Trump administration has ramped up pressure against China to do more to rein in North Korea’s illicit nuclear and ballistic missile programs.

North Korea conducted a ballistic missile test it is claiming as its first successful intercontinental ballistic missile test — which would mark a significant achievement for the rogue regime and what U.S. officials consider an urgent threat to the United States.

Trump is expected to speak to both Chinese President Xi Jinping and Japanese Prime Minister Shinzo Abe on Sunday, ahead of the Group of 20 summit in Hamburg, Germany, next week.