Two Chinese fighter jets intercepted a U.S. surveillance plane in the East China Sea on Wednesday amid larger diplomatic efforts over North Korea, the Air Force said.

The service said the crew members of the WC-135 nuclear-sniffing aircraft determined the Chinese pilots of the Su-30 jets were being "unprofessional." The encounter was still under investigation.

"The issue is being addressed with China through appropriate diplomatic and military channels," Pacific Air Forces spokeswoman Lt. Col. Lori Hodge said in a released statement.

The WC-135 Constant Phoenix is capable of detecting nuclear weapons activity and was deployed last month to Kadena Air Base on Japan's far southern island of Okinawa as the North Koreans were ramping up missile testing.

Since then, the Trump administration has been looking to China to pressure the regime of Kim Jong Un to give up its ambitions for a nuclear-tipped intercontinental ballistic missile that could reach the U.S. mainland.

However, there is deep friction between China and the U.S. over that country's territorial claims in the East China Sea, which includes the Korean peninsula and Japan.