North Korea has conducted four missile tests so far this year

A MARTINEZ, HOST:

Last year, it took North Korea nine months to conduct four missile tests. This year, it's taken them less than two weeks. These tests are banned by U.N. Security Council resolutions, but North Korea has made it clear that it's planning big upgrades to its nuclear arsenal. NPR's Anthony Kuhn reports from Seoul.

ANTHONY KUHN, BYLINE: Last Friday, North Korea claims to have launched two missiles from trains. Just hours earlier, it warned that it would respond to the Biden administration's sanctions on Pyongyang in connection with its missile programs. But Lee Ho-ryung, a researcher at the Korea Institute for Defense Analyses, a government think tank in Seoul, says the sanctions were just a convenient pretext to test weapons that were already in the works.

LEE HO-RYUNG: (Through interpreter) They are, in fact, testing weapons according to an existing plan, although the tests are presented as a reaction to events, such as South Korea's presidential election.

KUHN: Pyongyang could also test missiles to grab attention ahead of U.S. midterm elections this year. But Lee argues that plans to develop the missiles were laid three years ago, after then-President Donald Trump walked out on nuclear negotiations with the North's leader, Kim Jong Un. And some of those missiles are reaching the testing stage right about now.

LEE: (Through interpreter) It usually takes about three years from planning a weapon's development to testing it. So to calculate back, North Korea has used the time since the breakdown of the 2019 Hanoi summit to develop these weapons.

KUHN: Kim had already built and tested an atomic bomb and an ICBM in 2017, but he couldn't get what he wanted - security guarantees and relief from sanctions. So, Lee says, he decided to develop newer, more powerful weapons.

LEE: (Through interpreter) If North Korea posed a threat before, solely with its nuclear capability, now it pursues what will give it a second-strike capability.

KUHN: That means developing missiles that can evade initial enemy attacks, such as missiles launched from submarines and trains. North Korea also wants longer-range missiles that can reach all of the continental U.S. and carry multiple warheads. Kim Jong Un outlined a plan to develop such weapons in a January 2021 speech.

(SOUNDBITE OF ARCHIVED RECORDING)\

KIM JONG UN: (Non-English language spoken).

KUHN: "We must raise our defense, science and technology to a higher level," he said, "and carry out the goals and tasks of munitions production without fail." Kim's five-year plan ends in 2026.

Park Hyeong Jung, an emeritus researcher at the Korea Institute for National Unification, a Seoul-based government think tank, says Pyongyang is likely to unveil its biggest and most provocative weapons last.

PARK HYEONG JUNG: (Through interpreter) By 2023, '24 or '25, they will be able to actually test these weapons, but it's unlikely that they're completed yet. So between 2023 and 2025, a crisis could erupt.

KUHN: The Biden administration says it's open to an incremental deal that could offer some sanctions relief if Pyongyang limits its nuclear programs. It insists it has no hostile intent towards Pyongyang and is willing to talk anytime, anywhere. Pyongyang has rejected these overtures, and Park says it'll probably continue to do so until its plan is complete.

PARK: (Through interpreter) North Korea has to show off crucial new capabilities to diplomatically overwhelm the U.S. and South Korea. So until then, they're unlikely to come out to negotiate.

KUHN: Isolated by sanctions and the pandemic, North Korea faces economic hardships and chronic food shortages. But Park says that North Korea is determined to upgrade its arsenal, regardless of the cost.

Anthony Kuhn, NPR News, Seoul.

(SOUNDBITE OF LITTLE NORTH'S "HUNTRESS") Transcript provided by NPR, Copyright NPR.