The South Korean military scrambled stealth fighter jets after it detected mobilisation of 180 North Korean warplanes near the border between the two countries on Friday, reported news agency Reuters.
In a statement released by the South Korean military, North Korean aircraft carried out sorties north of the so-called tactical measure line, drawn to up 20 kilometres (12 miles) north of the Military Demarcation Line (MDL), reported the news agency.
Around 80 jets, including F-35A stealth fighters were scrambled by South Korea, in response to the North Korean sortie that was carried out between 11 am and 3 pm local time.
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While 240 aircraft participating in joint air exercise named Vigilant Storm with the United States continued with the drills.
The drills are taking place in response to the North's flurry of projectiles.
Pyongyang has called the joint air drills, "an aggressive and provocative military drill targeting" North Korea. It has also threatened that Washington and Seoul would "pay the most horrible price in history" if it continued, reported news agency AFP.
North Korea has launched a record-breaking blitz of missile launches this week.
More than 80 rounds of artillery were fired by North Korea into the sea overnight. It also launched multiple missiles on Thursday, including a possible failed intercontinental ballistic missile (ICBM), that landed near South Korea's territorial waters, reported Reuters.
South Korea called the missile launches a violation of a 2018 inter-Korean agreement.
US Defence Secretary Lloyd Austin described Pyongyang's ICBM launch as "illegal and destabilising". Both the countries also vowed to pursue new measures to demonstrate their "capabilities" against the North's growing threats, reported AFP.
(With input from agencies)