North Korea has tested parts of its biggest intercontinental ballistic missile in two recent launches, the U.S. and South Korean militaries said, a suggestion it is likely to fire that weapon soon to put a spy satellite into orbit in what would be its most significant provocation in years.

Separately, South Korea’s Defense Ministry said it detected signs that North Korea was possibly restoring some of the tunnels at its nuclear testing ground that were detonated in May 2018, weeks ahead of leader Kim Jong Un’s first summit with then- President Donald Trump. The ministry didn’t say whether it believes the North was restoring the site to resume tests of nuclear explosives.

North Korea’s neighbors detected two ballistic launches last week. North Korea later said it was testing cameras and other systems to be installed on a spy satellite but didn’t disclose what missiles or rockets it used.

After analyzing the launches, the U.S. and South Korean militaries concluded they involved an ICBM system under development that North Korea first unveiled during a military parade in October 2020.

“The purpose of these tests, which did not demonstrate ICBM range, was likely to evaluate this new system before conducting a test at full range in the future, potentially disguised as a space launch,” Pentagon press secretary John Kirby said in a statement Thursday.

South Korea released a similar assessment and said North Korea must immediately stop any act that raises tensions and regional security concerns.

The ICBM in focus is the Hwasong-17, North Korea’s biggest missile, which could potentially fly up to 15,000 kilometers (9,320 miles), far enough to strike anywhere in the U.S. and beyond. The 25-meter (82-foot) missile, which was shown again at a defense exhibition in North Korea’s capital, Pyongyang, last year, has yet to be test-launched.

North Korea has already demonstrated the potential to reach the U.S. mainland with flight tests of other ICBMs, the Hwasong-14 and Hwasong-15, in 2017. Some analysts say developing a larger missile could mean the country is trying to arm its long-range weapons with multiple warheads to overcome missile defense systems.

In 2018, North Korea unilaterally suspended long-range and nuclear tests before it entered now-dormant denuclearization talks with the United States. The talks collapsed in 2019 due to disputes over U.S.-led sanctions on the North. Top North Korean officials recently hinted at lifting the 2018 weapons test moratorium.

Seoul’s statement about North Korea’s nuclear testing ground came after recent commercial satellite images showed a possible resumption of construction activity at the site in the northeastern town of Punggye-ri. It was used for the North’s sixth and last nuclear test in 2017.

After declaring the site’s closure, Kim invited foreign journalists to observe the destruction of tunnels in May 2018. But North Korea didn’t invite outside experts to certify what had been destroyed. Analysts who studied the satellite images say it’s unclear how long it would take for the North to restore the site for nuclear detonations.

North Korea’s two missile launches were the latest in a string of tests in recent months, an apparent attempt to modernize its arsenal and pressure the Biden administration as nuclear disarmament talks remain stalled.

Observers expect North Korea to launch the Hwasong-17 missile for two main military purposes — testing key weapons parts and putting its first functioning spy satellite in space. They say North Korea may claim that it is firing a rocket, not a missile, for a satellite launch, but the U.N. and others have viewed past satellite launches as disguised tests of its long-range missile technology.

Kwon Yong Soo, a former professor at Korea National Defense University in South Korea, said the estimated thrust of the Hwasong-17 suggests it is powerful enough to place multiple reconnaissance satellites into orbit in a single launch. He said North Korea would also want to test the missile’s engine parts.

Kwon said the liquid-fueled Hwasong-17 may be too big and lack mobility given North Korea’s poor road conditions. He said the launch could be a show of force, but that a spy satellite could sharply increase the North’s capability to monitor the movements of U.S. aircraft carriers and other strategic assets.

“If you want to use long-range strikes on moving targets like aircraft carriers, you need to receive data on their movement from satellites,” Kwon said. “If North Korea puts a spy satellite (in space), that will be an epoch-making development.”

Jung Chang Wook, head of the Korea Defense Study Forum think tank in Seoul, said North Korea would want to test technologies that ensure multiple warheads of a missile could survive the extreme heat and pressure of reentry from space.

Jung and Kwon both believe North Korea has acquired the reentry vehicle technology for a single warhead missile, an assessment that some analysts dispute.

A spy satellite and a missile with multiple warheads were among an array of sophisticated weapons that North Korean leader Kim Jong Un has vowed to develop to counter what he calls American hostility such as economic sanctions.

“If North Korea succeeds in its test of a reentry vehicle for multiple warheads, that will tremendously boost its leverage in its negotiations with the United States,” Jung said. “It could be a game changer.”

On Friday, North Korean state media said Kim visited the country’s satellite launch facility and ordered officials to modernize and expand it to fire a variety of rockets. Earlier this week, he said that North Korea needs reconnaissance satellites to monitor “the aggression troops of the U.S. imperialism and its vassal forces.”

North Korea conducted two successful satellite launches from the Sohae Satellite Launching Ground in the northwest in 2012 and 2016. It said they were observation satellites under its peaceful space development program, but outside experts said they were designed to spy on rivals, though there is no evidence that the satellites ever transmitted images.

Experts say North Korea could launch a spy satellite ahead of a major political anniversary in April — the 110th birthday of state founder Kim Il Sung, the late grandfather of Kim Jong Un.

Jung, the analyst, said he thinks the launch will likely come in early May, just before a new South Korean president takes office later that month.

Kirby said the U.S. military ordered “enhanced readiness” among its ballistic missile defense forces in the region and intensified surveillance activities off the Korean Peninsula’s west coast.

The launch, if carried out, would be North Korea’s most serious provocative act since its three ICBM tests in 2017.

(AP)