Two Chinese fighter jets conducted an "unprofessional" intercept of a U.S. radiation-detecting plane in international airspace over the Yellow Sea off the Korean Peninsula, the U.S. military said Friday.

The U.S. aircraft, a U.S. WC-135 Constant Phoenix, known colloquially as a "nuke sniffer," was intercepted Wednesday by two Chinese Su-30 fighters during what the U.S. Air Force termed "a routine mission."

"The WC-135 was operating in accordance with international law," air force spokeswoman Lt. Col. Lori Hodge said. "While we are still investigating the incident, initial reports from the U.S. air crew characterized the intercept as unprofessional."