SEOUL, South Korea (AP) — South Korea scrambled about 80 military aircraft, including advanced F-35 fighter jets, on Friday after tracking about 180 flights by North Korean warplanes inside North Korean territory in what appeared to be a defiant show of strength.

North Korea’s mobilization of warplanes came after it test-fired around 30 ballistic missiles over the previous two days, including an intercontinental ballistic missile on Thursday that triggered evacuation warnings in Japan, in an angry response to ongoing joint exercises by hundreds of U.S. and South Korea military planes.

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 did not come particularly close to the Koreas’ border. The South Korean military spotted about 180 flight trails from 1 to 5 p.m., but it wasn’t immediately clear how many North Korean planes were involved and whether some may have flown more than once.

None of the planes breached the South Korean military’s virtual “tactical action” line, which is 20 to 50 kilometers (12 to 30 miles) north of the Koreas’ land and sea boundaries and is used for monitoring purposes to give the South enough time to respond to provocations or attacks.

South Korea still scrambled about 80 of its own warplanes, including an unspecified number of F-35 fighters. There weren’t any immediate reports of clashes.

U.S. and South Korean forces have been conducting joint “Vigilant Storm” aerial exercises involving about 240 warplanes, including F-35s. The exercises had been scheduled to end Friday, but the allies extended them to Saturday in response to North Korea’s intensified testing activity this week.

The extension of the drills was announced on Thursday after North Korea test-fired an ICBM, which triggered evacuation alerts and temporarily halted trains in northern Japan. It followed the launch by firing two short-range ballistic missiles into the sea.

Pak Jong Chon, a senior North Korean military official, then issued a statement threatening retaliation over the drills’ extension. North Korea subsequently fired three additional missiles into the sea and shot around 80 artillery rounds into the eastern parts of maritime buffer zones created by the rivals off their eastern and western coasts in 2018 as part of agreements to reduce tensions.

On Wednesday, North Korea fired more than 20 missiles, the most it has launched in a single day. Those launches came after Pak issued a veiled threat of a nuclear conflict with the United States and South Korea over their joint drills, which the North says are rehearsals for a potential invasion.

After already setting an annual record with dozens of ballistic missile launches in 2022, North Korea 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.

Experts say North Korea is attempting to force the United States to accept it as a nuclear power and seeks to negotiate economic and security concessions from a position of strength.