WASHINGTON (AP) — The U.S. and South Korea jointly warned North Korea on Thursday that use of any kind of nuclear weapon against Seoul or other regional allies would result in the end of Kim Jong Un's regime, as Pyongyang continued to rattle the peninsula with escalating missile tests.

North Korea has launched more than two dozen missiles over the last two days in response to U.S.-South Korean military exercises that began Monday. The launches have sent South Koreans scrambling for shelter and further frayed the nerves of a population already mourning the loss of more than 150 people at a horrific Halloween crowd crush.

Defense Secretary Lloyd Austin and South Korean Defense Minister Lee Jong-sup, after meeting Thursday at the Pentagon, released a joint statement saying they "strongly condemned" North Korea's escalating military flexing, including ballistic missile test launches, multiple rocket launches and coastal artillery.

Any use of nuclear weapons, including lower-yield tactical nuclear devices against Seoul or other regional allies such as Japan, would "result in the end of Kim Jong Un regime by the overwhelming and decisive response of the alliance," Lee said at a joint news conference with Austin.

Austin said North Korea's increased aggression would not result in additional U.S. troops or strategic assets being permanently relocated to the region but that Kim would see additional U.S. military presence rotating there.

In its launches Thursday, North Korea fired an intercontinental ballistic missile, drawing swift condemnation from the White House, which accused Pyongyang of "destabilizing the security situation in the region."

The U.S. and South Korea announced that the "Vigilant Storm" military exercise, which was scheduled to run through Friday, would be extended indefinitely.

Tensions between the U.S. and North Korea have also increased over newly declassified reports that it is providing artillery for Russia to use against Ukraine.

North Korea was shipping an undisclosed number of artillery shells to Russia but "trying to make it appear as though they're being sent to countries in the Middle East or North Africa," said National Security Council spokesman John Kirby.

North Korea has reacted to past U.S.-South Korean military drills with missile tests, which was one reason former President Donald Trump called for the exercises to cease for more than a year as he unsuccessfully negotiated with the North Korean leader to end his pursuit of nuclear weapons.

Large-scale U.S.-South Korean military exercises resumed this year. This fall's "Vigilant Storm" — which involves more than 1,600 U.S. and South Korean flights involving about 240 warplanes — is the largest such exercise to date, according to the Pentagon.

Pak Jong Chon, a secretary of the North's Workers' Party who is considered a confidant of Kim Jong Un, has called the U.S.-South Korean air force drills "aggressive and provocative."

"If the U.S. and South Korea attempt to use armed forces against (North Korea) without any fear, the special means of the (North's) armed forces will carry out their strategic mission without delay," Pak said, in an apparent reference to his country's nuclear weapons.

North Korea in recent months has been testing a string of nuclear-capable missiles and it adopted a law authorizing the preemptive use of its nuclear weapons in a broad range of situations. Some experts still doubt North Korea would use nuclear weapons first in the face of U.S. and South Korean forces.

The ballistic missile tests on Wednesday included at least 23 missiles as well as about 100 artillery shells that were fired into an eastern maritime buffer zone. South Korea's military said the 23 weapons were all short-range ballistic missiles or suspected surface-to-air missiles.

One of the ballistic missiles was flying toward South Korea's Ulleung island before it eventually landed 167 kilometers (104 miles) northwest of the island. South Korea's military issued an air raid alert on the island, according to the South's Joint Chiefs of Staff. South Korean media published photos of island residents moving to underground shelters.

Japanese Defense Minister Yasukazu Hamada said at least two ballistic missiles fired by North Korea showed a possibly "irregular" trajectory. This suggests the missiles were the North's highly maneuverable, nuclear-capable KN-23 missile, which was modeled on Russia's Iskander missile.

In response to the missile barrage, South Korea quickly launched its own missiles in the same border area.