A Chinese fighter jet carried out an "unsafe" intercept of a U.S. spy plane on routine patrol on Tuesday in international airspace over the East China Sea, according to U.S. Pacific Command.
The incident came as China again demanded an end to U.S. surveillance flights.
The intercept involved two Chinese J-10 fighter planes and a U.S. Air Force RC-135 reconnaissance plane, U.S. Pacific Command said in a statement.
"One of the intercepting Chinese jets had an unsafe excessive rate of closure on the RC-135 aircraft. Initial assessment is that this seems to be a case of improper airmanship, as no other provocative or unsafe maneuvers occurred," it added. The statement did not say how close the Chinese fighter came to the U.S. plane.
China's Defense Ministry said it had noted the report and was looking into it.
"Judging by the report, the U.S. side is again deliberately hyping up the issue of the close surveillance of China by U.S. military aircraft," it told Reuters in a statement.
"Chinese military pilots consistently carry out operations in accordance with the law and the rules, and are professional and responsible," it added, without elaborating.
Chinese Foreign Ministry spokesman Hong Lei said such patrols seriously harmed China's security, and repeated a demand they stop.
"China has the right to take defensive measures," he told a daily news briefing, without identifying the site of the intercept.
Asked if the incident had been timed to coincide with high-level China-U.S. talks in Beijing, attended by Secretary of State John Kerry, Hong responded, "Ask the Americans."
In May, the Pentagon said two Chinese fighter jets flew within 50 feet of a U.S. EP-3 aircraft over the South China Sea.
China has claimed most of the South China Sea, through which $5 trillion in trade is shipped every year. The Philippines, Vietnam, Malaysia, Taiwan and Brunei have overlapping claims.
Washington has accused Beijing of militarizing the South China Sea after creating artificial islands. Beijing, in turn, has criticized increased U.S. naval patrols and exercises in Asia.