South Korea put dozens of fighter jets and other warplanes on alert on Friday after detecting the mobilization of more than 180 North Korean warplanes in various locations.
This was reported in the Ministry of Defense of South Korea, Yonhap News reports.
South Korea raised about 80 planes into the air.
According to the Joint Chiefs of Staff, North Korean aircraft were detected between 11:00 a.m. and 3:00 p.m. over its interior and near the west and east coasts.
North Korea has strongly protested the ongoing Vigilant Storm joint air exercise between South Korea and the US.
The large-scale Vigilant Storm air force exercise involving more than 240 aircraft, including stealth aircraft, is underway amid growing concern that Pyongyang may soon conduct its first nuclear test since 2017.
North Korea fired three more short-range ballistic missiles toward the Sea of Japan on Thursday, shortly after South Korea and the United States decided to resume joint military exercises.