South Korea scrambled its jets on Friday after North Korea launched some 180 flights near the shared Military Demarcation Line dividing the two nations.
North Korean military forces were detected flying just north of the tactical line, also known as the Armistice Line, which was established in 1953 and formally ended the Korean War, first reported Reuters.
South Korea responded to the surge by scrambling 80 aircraft, including F-35A stealth fighters.
The aggressive show of force in North Korea’s air space came just hours after Washington and Seoul extended joint military drills, and some 240 aircraft continued with the largest ever U.S.-South Korea military exercises, dubbed "Vigilant Storm."
The drills were extended Thursday after Pyongyang launched a failed intercontinental ballistic missile test and fired at least six missiles into the sea.
Secretary of Defense Lloyd Austin took a stern tone when he and South Korea's Defense Minister Jong-Sup Lee announced the extended drills involving thousands of servicemen and told reporters that "at this time of heightened tension, our alliance is ironclad."
"We're returning to large scale exercises to strengthen our combined readiness and our ability to fight tonight if necessary," he added.
Seoul’s top defense official added that "any nuclear attack by the DPRK, including the use of tactical nuclear weapons, is unacceptable" and warned it could result in "the end of [the] Kim Jong un regime."
North Korea took issue with the joint military drills earlier in the week and fired the most missiles Pyongyang has ever launched in one day, directing 23 missiles toward South Korea Wednesday, with at least one landing near the shared sea border.
The show of force was the first time a short-range ballistic missile had landed near South Korea's territory since 1945, when the peninsula was divided.
The launches came hours after North Korea threatened to use nuclear weapons to get the U.S. and South Korea to "pay the most horrible price in history."