The South Korean military says it scrambled dozens of stealth fighter jets and other aircraft when its radar detected about 180 activities of North Korean warplanes on Friday.

The South Korean Joint Chiefs of Staff said the North Korean activities were detected over the North's inland areas as well as off the western and eastern coasts of the Korean Peninsula between around 11 a.m. and 3 p.m.

The Joint Chiefs said the air force scrambled more than 80 aircraft, including F-35A stealth fighters, even though the North's warplanes did not cross the line that would trigger such a response.

Military sources say the North's warplanes included bombers.

The South Korean military says it is maintaining a firm readiness for further provocations while closely monitoring moves by the North Korean forces in cooperation with the United States.

Yonhap News Agency says the North's move appears to be a response to the ongoing US-South Korean air drill. The exercise was originally scheduled to end on Friday, but was later extended until Saturday.