Terming the action as an "unprofessional" intercept, Air Force spokeswoman Lieutenant Colonel Lori Hodge said: "The issue is being addressed with China through appropriate diplomatic and military channels".
The WC-135 is a so-called "sniffer plane" created to scan the atmosphere for signs of nuclear activity.
In recent years, the sides have signed a pair of agreements aimed at preventing such encounters from sparking an worldwide crisis, as happened in April 2001 when a Chinese jet fighter collided with a US surveillance plane over the South China Sea, leading to the death of the Chinese pilot and China's detention of the 24 USA crew members for 10 days.
While on a routine mission, two Sukhoi Su-30 fighter aircrafts intercepted the USA "sniffer" as it flew over the East China Sea.
'US military aircraft routinely transit global airspace throughout the Pacific, including the East China Sea, ' she said.
"Distances always have a bearing on how we characterize interactions", said Hodge.More news: Alexis Sanchez states his prediction for Arsenal v Chelsea
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Two Chinese fighter jets intercepted a U.S. Air Force radiation detection plane Wednesday in a maneuver U.S. officials called "unprofessional".
We will remind, earlier it became known that on may 14 North Korea has carried out another test launch of a ballistic missile a few days after the inauguration of the new President in South Korea. At that time the US called the incident unsafe. On Feb. 8, a U.S. Navy P-3 spy plane and a Chinese military aircraft flew closely to each other over the South China Sea.
Last June, two Chinese J-10 fighter planes intercepted a U.S. Air Force RC-135 reconnaissance plane over the East China Sea.
China's Ministry of National Defense did not immediately respond to a request for comment.
At the time, the United States military said its maritime reconnaissance aircraft was carrying out a routine patrol in the area.
China is deeply suspicious of any U.S. military activity in the resource-rich South China Sea, parts of which are disputed by China and its smaller neighbors including the Philippines, Vietnam and Malaysia.