Two military aircraft from China and the U.S. had an “unsafe” encounter over a disputed part of the South China Sea, the U.S. Pacific Fleet said on Friday, the first publicly confirmed incident since May last year.

A People’s Liberation Army Air Force KJ-200 surveillance plane had “an interaction characterized by U.S. Pacific Command as ‘unsafe’” with a Navy P-3C Orion surveillance aircraft, Pacific Command spokesman Major Robert Shuford said in an e-mail. CNN earlier reported the planes flew within 1,000 feet of each other in the general vicinity of the Scarborough Shoal.

“We will address the issue in appropriate diplomatic and military channels,” Shuford said. “The U.S. Navy P-3C was on a routine mission operating in accordance with international law.”

An unidentified defense ministry official told the state-run Global Times the Chinese pilots took legitimate and professional measures to deal with the encounter. The official added the U.S. should seek to minimize air or sea incidents with China, according to the report.

Tensions between the U.S. and China are elevated as President Donald Trump threatens higher tariffs on Chinese products and questions the U.S. approach to Taiwan, which Beijing considers part of its territory. In his confirmation hearings, Secretary of State Rex Tillerson said the U.S. should deny China access to artificial reefs it built in the South China Sea.

***Drone Seizure***

Two Chinese fighters intercepted a surveillance plane last May over international waters in the northern part of the South China Sea, coming within 50 feet and forcing the U.S. pilot to descend, according to the Pentagon. China said its aircraft were flying near Hainan, its island gateway to the South China Sea, at a safe distance from the reconnaissance plane.

The area around the Scarborough Shoal is particularly sensitive because China seized the reef from the Philippines in 2012. China claims about 80 percent of the South China Sea. In December, a Chinese navy ship grabbed a U.S. Navy underwater drone operating in the vicinity. It was eventually returned.

An international tribunal last year ruled China’s claims have no legal standing. China says the tribunal has no jurisdiction.

Since that ruling there has been speculation China could seek to build on the Scarborough Shoal and extend its land reclamation to the north of the Spratlys, where it has constructed features on seven rocks and reefs and built three airstrips capable of handing military aircraft. U.S. Defense Secretary James Mattis last week said diplomatic efforts should be exhausted to resolve disputes over the South China Sea.

The Philippines and Vietnam are among other claimants. Mattis also accused China of "shredding the trust" of its neighbors."Our military stance should be one that reinforces our diplomats," he said, adding "at this time we do not see any need for dramatic military moves at all."