South Korea's F-35 A Stealth fighter jets participate in the media day for the 74th anniversary of Armed Forces Day at the military base in Gyeryong-City, South Korea, on Sept. 29, 2022. JEON HEON-KYUN / POOL PHOTO VIA AP, FILE

South Korea scrambled dozens of military aircraft, including advanced F35 fighter jets, after spotting 180 North Korean warplanes flying in North Korean territory Friday in what appeared to be a defiant show of strength.

North Korea's aerial exercises came after the North test-fired around 30 ballistic missiles during the two previous days, including an intercontinental ballistic missile on Thursday that triggered evacuation warnings in Japan, in an angry response to U.S.-South Korea joint air force drills involving hundreds of their warplanes.

South Korea's Joint Chiefs of Staff said the North Korean warplanes were detected in various areas inland and along the country's eastern and western coasts but didn't come particularly close to the inter-Korean border.

None of the planes breached the South Korean military's virtual "tactical action" line 12 to 31 miles north of the Koreas' land and sea boundaries for monitoring purposes to give the South enough time to respond to provocations or attacks.

The South still scrambled 80 of its own warplanes but there weren't any immediate reports of clashes.

U.S. and South Korean forces were also separately conducting their "Vigilant Storm" combined aerial exercise, which involved some 240 warplanes, including F35s. The training had been scheduled to last through Friday, but the allies extended it to Saturday in response to North Korea's intensified testing activity this week.

The extension of the drills was announced on Thursday after the North test-fired an ICBM, which triggered evacuation alerts in northern Japan, and followed that with two short-range ballistic missile launches into sea.

A senior North Korean military official issued a statement threatening retaliation over the extension of the drills, and the North about an hour later fired three additional missiles into the sea.

On Wednesday, North Korea fired more than 20 missiles, the most it has launched in a single day.

After already setting an annual record with dozens of ballistic missile launches in 2022, Pyongyang has further dialed up its testing activity since late September, including what it described as simulated nuclear attacks on South Korean and U.S. targets. It has said its tests are meant as a warning against the United States' military drills with allies South Korea and Japan that it portrays as rehearsals for a potential invasion.

Experts say North Korea is escalating brinkmanship aimed at forcing the United States to accept it as a nuclear power and at negotiating economic and security concessions from a position of strength.

U.S. and South Korean officials tell CBS News North Korean leader Kim Jong Un is preparing to carry out an atomic test soon as it continues to develop a tactical nuclear weapon. A nuclear test would signal that Kim has managed to grow his weapons program through the Trump and Biden administrations and despite the COVID-19 pandemic.

"We think they're ready to go. Kim just has to give the thumbs up," a senior U.S. State Department official told CBS News.

A tactical nuclear device is designed to potentially be used on a battlefield.

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