The South Korean air force scrambled fighter jets and issued a warning after identifying two Russian planes at around 1.41pm on Friday, according to a text message sent to reporters from the Korean Joint Chiefs of Staff. The Russian planes entered the zone three more times during Friday afternoon, passing over the Korea’s east coast and waters near the country’s southernmost island of Jeju.

South Korea’s defense ministry complained about the infringement on the Korean defense zone at a meeting with Andrey P. Falileev, a Russian colonel in Seoul, Yonhap News Agency reported on Saturday, citing the ministry. The Russian planes were said to be TU-95 long-range strategic bombers, Yonhap reported without citing anyone.

Russian planes entered the defense zone several times this year but it is the first time they have done it multiple times in a day, Yonhap reported, citing an unidentified official at Korean Joint Chiefs of Staff. A Chinese military plan flew into the zone three times in 2018, claiming it was a regular drill.