South Korea's foreign ministry called in the ambassador from China Saturday night after a Chinese military plane trespassed into South Korea's air defense identification zone earlier the same day.
According to officials at the foreign ministry, deputy foreign minister Yoon Soon-gu summoned ambassador Qiu Guohong and called on Beijing to find ways to stop such incursions from happening again.
The South Korean defense ministry has also responded.
The ministry says it called in China's defense attache in Seoul and lodged a stern protest.
According to South Korea's Joint Chiefs of Staff, the Chinese aircraft, believed to be a reconnaisance plane, came close to the southeastern city of Pohang.
The Chinese side is said to have claimed that it was part of a "normal" flight training in international airspace.