Two Chinese fighter jets conducted an "unprofessional" intercept of a U.S. aircraft in international airspace over the East China Sea on Wednesday, according to the U.S. Air Force.
The American aircraft was conducting a routine mission in accordance with international law when the two Chinese SU-30 jets made the move, Pacific Air Forces spokeswoman Lt. Col. Lori Hodge told NPR.
One of the SU-30s flew upside down directly above the U.S. plane and both of the Chinese jets came within 150 feet of it, CNN reports.
Hodge said the crew aboard the American plane described the move as unprofessional due to its speeds and proximity.
The U.S. aircraft, a WC-135 Constant Phoenix, is used by the Air Force to detect atmospheric traces of nuclear explosions. The WC-135 have been used in the past to collect evidence of North Korean nuclear tests, according to CNN.
"In 2013, China declared an air defense identification zone over much of the East China Sea and it requires foreign aircraft in the area to follow its orders," NPR's Anthony Kuhn reports. "The U.S. refuses to recognize the zone, and it is unclear whether the incident took place in it."
Hodge said the U.S. aircraft was "conducting a routine mission in international airspace over the East China Sea. The WC-135 was operating in accordance with international law."
The incident comes at a time when China and the Trump administration have apparently agreed to cooperate on the North Korean nuclear issue.
Wednesday's encounter isn't the first close call this year. In February, CNN reported on an "unsafe" encounter over the South China Sea when a U.S. Navy P-3 Orion reportedly had to change course to avoid colliding with a Chinese surveillance plane — and that a U.S. official said the aircraft came within 1,000 feet of each other.
As for Wednesday's intercept, Hodge said "we are not providing more specifics as we would rather discuss it privately with China through our Military Maritime Consultative Agreement meeting and through diplomatic channels. This will allow us to continue building confidence with our Chinese counterparts on expected maneuvering to avoid mishaps."