North Korea fired two short-range ballistic missiles into its eastern sea early Wednesday in what appeared to be a statement of defiance as the United States deployed a nuclear-armed submarine to South Korea for the first time in decades.

The launches came as the U.S.-led United Nations Command tries to secure the release of a U.S. soldier who fled to North Korea from the South Korean side of a border village Tuesday afternoon.

Private 2nd Class Travis King, in his early 20s, had just been released from a South Korean prison where he was held on assault charges. Instead of getting on a plane to be taken back to Fort Bliss, Texas, he left and joined a tour of the Korean border village of Panmunjom, where he ran across the border, U.S. officials say.

Kim vows to boost North Korea's nuclear capability after observing new ICBM launch

South Korea’s Joint Chiefs of Staff said that from 3:30 to 3:46 a.m. North Korea fired two short-range ballistic missiles from an area near capital Pyongyang that flew about 550 kilometers (341 miles) before landing in waters east of the Korean Peninsula.

Those flight details were similar to the assessment of the Japanese military, which said the missiles landed outside of Japan’s exclusive economic zone and that there were no immediate reports of damage from ships or aircraft in affected areas.

The flight distance of the North Korean missiles roughly matched the distance between Pyongyang and the South Korean port city of Busan, where the USS Kentucky arrived Tuesday afternoon in the first visit by a U.S. nuclear-armed submarine to South Korea since the 1980s.

Japanese Defense Minister Yasukazu Hamada told reporters that the North Korean missiles traveled on a low trajectory, with their maximum altitude reaching about 50 kilometers (31 miles), and possibly demonstrated “irregular maneuver” in flight.

North Korea launches long-range missile toward sea after making threat over alleged US spy flights

Japan has previously used similar language to describe the flight characteristics of a North Korean weapon modeled after Russia’s Iskander missile, which travels at low altitudes and is designed to be maneuverable in flight to improve its chances of evading missile defenses.

The South Korean Joint Chiefs of Staff condemned the North Korean launches as “major provocation” that threatens peace and stability in the region and said the South Korean and U.S. militaries were closely monitoring the North for further weapons activities.

North Korea opens key party meeting to tackle its struggling economy and talk defense strategies

Wednesday’s launches marked the North’s first ballistic activity since July 12, when it flight-tested a new solid-fuel intercontinental ballistic missile that demonstrated potential range to reach deep into the U.S. mainland. That launch was supervised by the country’s authoritarian leader Kim Jong Un, who vowed to further bolster his country’s nuclear fighting capabilities in the face of expanding U.S.-South Korean military activities, which he blamed for worsening the security environment on the Korean Peninsula.

Tensions have rose in the region in recent months as the pace of both North Korean weapons tests and U.S.-South Korean joint military drills have increased in a cycle of tit-for-tat.

Since the start of 2022, North Korea has test-fired around 100 missiles while attempting to demonstrate a dual ability to conduct nuclear attacks on both South Korea and the continental United States. The allies in response have stepped up their joint military training and agreed to increase the deployments of U.S. strategic assets like long-range bombers, aircraft carriers and submarines to the region.

Periodic visits by U.S. nuclear ballistic missile-capable submarines to South Korea were one of several agreements reached by U.S. President Joe Biden and South Korean President Yoon Suk Yeol in April in response to North Korea’s expanding nuclear threat. They also agreed to further expand combined military exercises, strengthen joint planning for nuclear contingencies and establish a bilateral Nuclear Consultative Group, which held its inaugural meeting in Seoul Tuesday.

The steps were meant to ease South Korean concerns about North Korea's growing nuclear weapons arsenal and suppress voices within the South calling for the country to pursue its own nuclear weapons program.

U.S. Forces Korea said in a statement that the Kentucky's arrival in Busan reflects the United States' “ironclad” commitment to “extended deterrence,” referring to an assurance to defend its ally with its full military capabilities, including nuclear ones.

The Ohio-class submarine can be equipped with about 20 Trident II ballistic missiles with a range of 12,000 kilometers (7,456 miles), according to South Korea's military.

“From this submarine, the U.S. can launch attacks (on North Korea) from anywhere in the world," said Moon Keun-sik, a submarine expert who teaches at Kyonggi University in South Korea. “But there will likely be backlashes from North Korea and China because it’s like the world’s most covert and threatening nuclear weapons forces being deployed on their doorsteps.”

While some South Korean conservatives have expressed disappointment that the Biden-Yoon meeting in April came short of agreeing to station U.S. nuclear weapons or strategic assets in the South, placing nuclear weapons offshore and on submarines is “actually a stronger deterrent in many ways,” said Duyeon Kim, a senior analyst at Washington’s Center for a New American Security.

“Deterrence is strengthened when the location of American strategic assets is unknown to the adversary as long as the adversary knows that these weapons exist,” said Kim.

Still, Seoul and Washington will need to find the “sweet spot” when it comes to the visibility of America’s extended deterrent.

“Too much visibility of strategic assets could actually undermine the deterrent effect while too little could raise questions in Seoul about commitment," Kim said.