Beijing accused Washington of "hype" on Wednesday after the US said two Chinese jets conducted an unsafe intercept of one of its spy planes over the East China Sea.

The spat came soon after the world's two largest economies concluded an annual dialogue overshadowed by disagreements over maritime issues.

US Pacific Command spokesman Commander David Benham said two Chinese J-10 fighter jets flew close to an American RC-135 reconnaissance plane that was on a routine patrol.

The Pentagon downplayed the encounter and blamed it on shoddy piloting.

"One of the intercepting Chinese jets had an unsafe excessive rate of closure on the RC-135 aircraft," Benham said, without specifying exactly where the incident occurred.

"The US once again is deliberately hyping this issue," Chinese foreign ministry spokesman Hong Lei told a regular briefing on Wednesday.

"The relevant Chinese military personnel have always acted professionally and in accordance with law."

He also called on the US to stop carrying out "close surveillance activity against China...to prevent similar incidents from happening again".

The East China Sea is part of the Pacific and home to small islands whose ownership is disputed by China, Japan and Taiwan.

China also claims a string of islets across the South China Sea and its military expansion in the contested waterway has sparked heightened tensions with regional neighbours and the United States.

Pentagon chief Ashton Carter attended a security summit in Singapore over the weekend, promising unspecified "actions" if China continued its buildup.

Last month the Pentagon said two Chinese jets conducted an "unsafe" intercept of a US reconnaissance plane over the South China Sea.

Still, PACOM head Admiral Harry Harris told reporters in Singapore on Saturday that such incidents were rare.

Tuesday's reported intercept came as US Secretary of State John Kerry urged China to settle its territorial rows peacefully and based on the "rule of law" on a visit to Beijing.

Beijing will not budge on its claims of ownership over a vast tranche of the South China Sea, a top official insisted Tuesday, as a key two-day annual meeting ended in the Chinese capital.