Beijing has demanded an end to US surveillance near China after two of its fighter jets carried out what the Pentagon said was an "unsafe" intercept of a US military reconnaissance aircraft over the South China Sea.
The incident, likely to increase tension in and around the contested waterway, took place in international airspace on Tuesday as the plane carried out "a routine US patrol," a Pentagon statement said.
A US Defence official said two Chinese J-11 fighter jets flew within 50 feet (15 metres) of the US EP-3 aircraft.
The official said the incident took place east of Hainan island.
"Initial reports characterised the incident as unsafe," the Pentagon statement said.
"It must be pointed out that US military planes frequently carry out reconnaissance in Chinese coastal waters, seriously endangering Chinese maritime security," China's Foreign Ministry spokesman Hong Lei Hong told reporters.
"We demand that the United States immediately cease this type of close reconnaissance activity to avoid having this sort of incident happening again," Hong said.
Speaking at a regular press briefing, he described the Pentagon statement as "not true" and said the actions of the Chinese aircraft were "completely in keeping with safety and professional standards."
"They maintained safe behaviour and did not engage in any dangerous action," Hong said.
The encounter comes a week after China scrambled fighter jets as a US Navy ship sailed close to a disputed reef in the South China Sea.
Another Chinese intercept took place in 2014 when a Chinese fighter pilot flew acrobatic manoeuvres around a US spy plane.
The intercept occurred days before President Barack Obama travels to parts of Asia from May 21-28, including a Group of Seven summit in Japan and his first trip to Vietnam.
China claims most of the South China Sea, through which US$5 trillion (NZ$7.39 trillion) in ship-borne trade passes every year. The Philippines, Vietnam, Malaysia, Taiwan and Brunei have overlapping claims.
Washington has accused Beijing of militarising the South China Sea after creating artificial islands, while Beijing, in turn, has criticised increased US naval patrols and exercises in Asia.
The Pentagon statement said the Department of Defence was addressing the issue through military and diplomatic channels.
China's Defence Ministry said in a fax that it was looking into reports on the incident.