The sources said that aircraft global positioning system (GPS) distracted by an electronic signal when flying over Haeju and Kaesong in North Korea.
That drone aircrft took part in joint military exercises US-South Korea.
The incident was not disclosed in reports submitted by the Department of Defense of South Korea's to parliamentary defense committee members, Ahn Kyu-Baek.
Both the U.S defense ministry and South Korea defense ministry declined to comment on this report
