WASHINGTON: The Pentagon on Friday said it was concerned by an "unsafe and unprofessional" encounter between two Chinese fighters and a US surveillance plane over the South China Sea.

"The aircrew deemed the intercept unsafe and unprofessional. Operations were able to continue unimpeded," he said.

"We continue to review the facts of this incident and will convey our concerns through appropriate channels with the Chinese government."

On Thursday, a United States destroyer sailed in disputed South China Sea waters near a reef claimed by Beijing in the first "freedom of navigation" exercise under President Donald Trump.

The maneuvers come ahead of a major regional security summit in Singapore next week.

According to Pentagon spokesman Commander Gary Ross,  the Chinese J-10 warplanes intercepted the American Navy P-3 that was operating in international airspace late on May 24.