The U.S. carried out its fourth Freedom of Navigation Operation (FONOP) in the South China Sea under President Trump near islands claimed by China, prompting anger in Beijing and a military reaction from Chinese naval forces.

Reuters reports exclusively, citing three unnamed U.S. sources, that the operation involved the USS Chafee, a destroyer that operations 100 percent on biofuels:

The operation was the latest attempt to counter what Washington sees as Beijing’s efforts to limit freedom of navigation in the strategic waters. But it was not as provocative as previous ones carried out since Trump took office in January.

The officials, speaking on condition of anonymity, said the Chafee, a guided-missile destroyer, carried out normal maneuvering operations that challenged “excessive maritime claims” near the Paracel Islands, among a string of islets, reefs and shoals over which China has territorial disputes with its neighbors.

China’s Defense Ministry said on Wednesday that a warship, two fighter jets and a helicopter had scrambled to warn the U.S. ship away, adding it had infringed upon China’s sovereignty and security with its “provocation.”

Trump is attempting to influence China to take a harder line against its ally, North Korea, in an attempt to thwart Pyongyang’s efforts in obtaining a credible nuclear weapons capability. So far China’s record has been mixed: It has approved of new sanctions at the UN Security Council, which it could have blocked with a veto, and has closed off some economic and trade avenues for Pyongyang. So some believe the U.S. Navy FONOPs are going to undermine any progress the administration has made with Beijing regarding North Korea.

Meanwhile, China’s foreign ministry said: “China will continue to take resolute measures to protect Chinese sovereign territory and maritime interests. China urges the U.S. to conscientiously respect China’s sovereign territory and security interests, conscientiously respect the efforts regional countries have made to protect peace and stability in the South China Sea, and stop these wrong actions.”

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