A Chinese fighter jet conducted a barrel roll over a U.S. Air Force reconnaissance plane flying in global airspace above the Yellow Sea on Wednesday, according to a U.S. official.
The U.S. aircraft, a WC-135 Constant Phoenix, is commonly referred to a "sniffer" because it detects signs of nuclear activity in the atmosphere by "sniffing".
The aircraft uses external flow-through devices that collect air and debris samples that are later sent to a lab for analysis.
"While we are still investigating the incident, initial reports from the USA aircrew characterized the intercept as unprofessional", Hodge said. "The issue is being addressed with China through appropriate diplomatic and military channels", Hodge said.
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The US WC-135 plane was on a mission to detect radiation in global airspace over the East China Sea.
In the second case, a Chinese J-10 fighter came within 100 feet of a U.S. Navy RC-135 reconnaissance aircraft.
China is deeply suspicious of any USA military activity in the resource-rich South China Sea.
Donald Trump's administration has been ratcheting up pressure on nuclear-armed North Korea to give up its military ambitions. A Chinese Shaanxi KJ-200 aerial warning and control aircraft flew within 1,000 feet of a U.S. Navy P-3C Orion surveillance aircraft in February, forcing the latter to alter course.
After the February incident, USA officials said close encounters between USA and Chinese forces are extremely rare, with no such incidents in 2015 and two in 2016.