U.S. bombed Iran’s deepest nuclear sites. Should North Korea be worried?

When U.S. President Donald Trump ordered airstrikes on three of Iran’s key nuclear facilities on June 22 — including the heavily fortified Fordow site — it sent an unmistakable message to countries pursuing hidden nuclear programs: even the deepest bunkers are no longer safe. For North Korea, which has based much of its nuclear and command infrastructure underground, the implications are likely profound.

Though the geopolitical contexts differ, analysts say Pyongyang is now likely reassessing the vulnerability of its subterranean defenses.

Iran had relied on mountainous terrain and reinforced concrete to protect its facilities, with Fordow said to be buried nearly 90 meters (295 feet) underground. Yet, according to Trump, whose administration ordered the strikes, Fordow “is gone.”

North Korea has long prided itself on its vast network of underground military infrastructure. After experiencing massive aerial attacks by the UN forces led by the United States during the Korean War, North Korea is said to have built over 6,000 underground facilities, mostly in granite areas to fortify the entire country.

Late Hwang Jang-yop, former secretary of the Central Committee of the Workers’ Party of North Korea who defected to South Korea, said that there is a huge hidden bunker 300 meters underground in Pyongyang and that the North Korean command hides there in case of emergency.

South Korean and U.S. intelligence also believe that the North’s weapons of mass destruction (WMD) sites — including for nuclear and missile production and storage — are underground. Its nuclear sites — Yongbyon, Punggye-ri, and the uranium enrichment facility at Kangson — are among the most well-known examples. Around Pyongyang, analysts suspect the regime has concealed warhead storage and possibly intercontinental ballistic missiles (ICBMs) in tunnels, with reports pointing to the Mangyongdae district as a hub of such activity.

A military official who requested anonymity pointed out that during “a December 2023 missile test, South Korean officials took note of a transporter erector launcher for the Hwasong-18 emerging from a tunnel along an unpaved road,” suggesting the missile was deployed from a hidden facility.

For Pyongyang, the fear is no longer just theoretical. If Iran’s fortified infrastructure could be reduced to rubble, then North Korea’s hardened bunkers — despite years of construction and concealment — may be just as vulnerable. Washington and Seoul have long rehearsed strike scenarios targeting North Korean nuclear assets.

After the failed Hanoi summit in 2019, Trump reportedly identified five undisclosed North Korean nuclear sites, signaling that U.S. intelligence may already have the coordinates of critical targets.

Adding to Pyongyang’s unease is a recent social media post by Trump on June 17, in which he claimed to know the whereabouts of Iran’s Supreme Leader Ayatollah Ali Khamenei, calling him “an easy target” and demanding unconditional surrender. Reports later emerged that Khamenei had named three successors in case of assassination — details that are likely to alarm Kim Jong-un.

Kim’s fear is also stoked by the sense that the United States can observe his every move through advanced intelligence assets, including satellites. This “siege mentality” may compel Kim to rely even more heavily on underground hideouts and bunkers to ensure regime continuity.

Iran, like North Korea, chose mountainous terrain for its nuclear facilities. Fordow, in particular, had been regarded as impenetrable due to its location 80 to 90 meters underground. Yet even such fortification proved insufficient. In a nationally televised address, Trump claimed the United States had bombed Fordow, Natanz and Isfahan and successfully eliminated Iran’s key uranium enrichment infrastructure — potentially setting Iran’s nuclear program back by more than a decade.

For North Korea, this raises serious questions about the durability of its prized underground shield. The bunker-busting weapon used in the Fordow strike, the GBU-57, has been in U.S. possession since 2011 but had never been used in combat. Weighing over 13 tonnes (28,660 pounds), it can penetrate more than 60 meters of reinforced concrete and is launched from a B-2 stealth bomber. Its full name — Guided Bomb Unit-57 Massive Ordnance Penetrator — reflects its status as the most powerful nonnuclear bomb in the U.S. arsenal.

Until now, the GBU-57 had been classified as a deterrent weapon. Its combat debut in the Fordow strike suggests that the United States not only had the will to use it but had meticulously planned for the operation. Despite early doubts that the GBU-57 could destroy Fordow — given its depth — U.S. forces reportedly dropped six bombs to achieve the objective. Trump later posted on social media, “FORDOW IS GONE,” reinforcing the impression of total destruction. Israeli officials, who had long argued that only the GBU-57 could breach Fordow, had persistently called for U.S. involvement.

But North Korea has more than one reason to worry. Beyond the GBU-57, it also faces the growing threat of South Korea’s indigenous Hyunmoo-Ⅳ and Hyunmoo-Ⅴ missiles. Though their full specifications remain classified, defense insiders suggest that the Hyunmoo-Ⅴ’s warhead weighs around 8 tons — four times heavier than its predecessor — and may be capable of penetrating over 100 meters underground. Unlike the GBU-57, which must be airdropped, the Hyunmoo series can be launched from the ground in large numbers, potentially giving them an edge in saturation strikes.

In a combined operation, dozens of Hyunmoo missiles flying at hypersonic speeds alongside U.S. bunker busters could target North Korea’s nuclear facilities and leadership shelters simultaneously — leaving the regime with few options. The South Korean military is reportedly producing hundreds of these missiles for active deployment.

That growing pressure was not lost on Pyongyang. In 2023, then President Yoon Suk Yeol prominently featured the Hyunmoo-Ⅳ at a national military parade, followed by the public unveiling of the Hyunmoo-Ⅴ during the 2024 Armed Forces Day ceremony. These moves were interpreted as direct warnings against North Korea’s ICBM tests and provocations such as launching balloons laced with waste into the South. In response, Kim Yo-jong, the powerful sister of Kim Jong-un, released a statement mocking the missiles as “grotesque fakes” and “gaudy frauds” — a reaction that, according to South Korean defense officials, only betrayed Pyongyang’s fear.

For North Korea, the reality after Iran’s devastating strike is stark: its once-vaunted underground sanctuaries are no longer guarantees of safety. In a world of precision bombs, hypersonic missiles and real-time satellite surveillance, the very foundation of its security doctrine is under pressure — perhaps more than ever before.

BY CHUNG YEONG-GYO, LEE KEUN-PYUNG [yim.seunghye@joongang.co.kr]