South Korea's defense minister has lodged a protest with the U.S. Forces Korea (USFK) early this week over its brief standoff with Chinese fighter jets during a rare air exercise, military sources said Saturday. Defense Minister Ahn Gyu-back has delivered a complaint in a call with Gen. Xavier Brunson, the commander of the Combined Forces Command and the United States Forces Korea, immediately after he received a report of the incident on Wednesday, according to the sources. Gen. Jin young-sung, the chairman of the Joint Chiefs of Staff, also lodged a complaint in a call with Gen. Brunson, they added. On Wednesday, U.S. and Chinese fighter jets engaged in a rare standoff over the Yellow Sea during a training operation of the U.S. Air Force, which involved some 10 USFK F-16 fighter jets. The F-16 jets reportedly flew to an area between the respective air defense identifications zones of South Korea and China, prompting the Chinese military to dispatch its own fighter jets to the scene, but no clash occurred. The USFK had notified the South Korean military of its plan ahead of the exercise