According to US Pacific Command spokesman Commander David Benham, two Chinese J-10 fighter jets flew close to an American RC-135 reconnaissance plane that was on a routine patrol.
US Air Force plane intercepted by Russian jet in 'unsafe' manner: Pentagon
"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.
"Initial assessment is that this seems to be a case of improper airmanship, as no other provocative or unsafe maneuvers occurred."
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 neighbors and the United States.
Tuesday's intercept came as US Secretary of State John Kerry visited Beijing and urged China to settle its territorial rows peacefully and based on the "rule of law."
Chinese jets intercept US military plane over South China Sea: Pentagon
Pentagon chief Ashton Carter attended a security summit in Singapore over the weekend, promising unspecified "actions" if China continued its buildup.
On May 17, the Pentagon said two Chinese jets conducted another "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.
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