May 18 (UPI) -- Two Chinese fighter jets intercepted a U.S. Air Force radiation detection plane Wednesday in a maneuver U.S. officials called "unprofessional."
The Sukhoi Su-30 jets came within 150 feet of the WC-135 Constant Phoenix aircraft, which "sniffs" the atmosphere for signs of nuclear activity.
One of the Chinese jets flew inverted, or upside down, above the U.S. plane -- similar to a maneuver in the movie Top Gun -- in international airspace over the East China Sea.
The U.S. planes routinely gather evidence of possible nuclear tests by North Korea.
"While we are still investigating the incident, initial reports from the U.S. aircrew characterized the intercept as unprofessional," Air Force Lt. Col. Lori Hodge said in a statement. "The issue is being addressed with China through appropriate diplomatic and military channels."
The incident was the second between U.S. and Chinese aircraft this year.
In February, U.S. officials said a U.S. Navy P-3 Orion aircraft and a Chinese KJ-200 plane had an "unsafe" close encounter in the South China Sea, flying within 1,000 feet of each other.