SEOUL, South Korea — Mounting reports that North Korea is set to be the first outside power to directly intervene in the Russia-Ukraine conflict are posing perhaps the most serious challenge yet to the U.S. and its allies from the “axis” of authoritarian states looking to overturn the global security order.

The tension escalated again Monday when the South Korean government summoned the Russian ambassador in Seoul to protest “in the strongest possible terms” the reports that thousands of North Korean troops are deploying to a Russian military base for training and potentially to the front lines in Ukraine.

The Russian Embassy insisted that warming relations between Moscow and Pyongyang are not “directed against South Korean security interests.”

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South Korea’s lead spy agency on Friday said it had hard proof that the regime of North Korean leader Kim Jong-un sent 1,500 special operation forces to Russia this month to support Moscow’s war against Ukraine. That followed claims from Ukrainian intelligence analysts that 11,000 North Koreans were training in Russia, prior to a battlefield deployment.

South Korean intelligence agencies now estimate that 12,000 North Korean troops, enough to man an infantry division and a special forces brigade, are being dispatched.

For months, multiple intelligence sources have shown that Pyongyang is massively arming Russia, but the troop deployment would mark a new level of commitment and coordination.

In a surprise visit, U.S. Defense Secretary Lloyd Austin traveled to Kyiv Monday to meet with Ukrainian President Volodomyr Mr. Zelenskyy, expressing support for the country’s war with Russia. North Korea will almost certainly be on the agenda.

“A new threat has emerged — the malign alliance between Russia and North Korea,” Mr. Zelenskyy said via video on Sunday evening. “If the world remains silent now, and if we face North Korean soldiers on the front lines, … it will benefit no one in this world and will only prolong this war.”

The North Korean deployment could shatter a number of precedents in the global security order.

Geopolitically, any actual combat alliance between the two continental, authoritarian powers would far outstrip the modest, nonbinding security links forged between Atlantic and Pacific democracies in recent years. It would also alter the dynamics within to the emerging “axis of authoritarianism,” demonstrating that heavily sanctioned North Korea, already exporting weapons and munitions to heavily sanctioned Russia, is more risk-tolerant than China or Iran.

Tactically, the deployment could provide the Kremlin with fresh forces along the 600 miles of front lines in eastern and southern Ukraine.

For North Korea, the move marks the nation’s first-ever overseas expeditionary force. Its prior overseas adventures were limited to tiny — and deniable – presences: pilots, military advisers, special forces.

“It would be serious and push the conflict into a new stage, an additional escalatory stage,” warned French Foreign Minister Jean-Noel Barron on a visit to Kyiv over the weekend.

His Ukrainian counterpart, Andrii Sybiha, called it “a huge threat,” adding a risk exists of the war “growing out of its current scale and borders.”

Military historian Gastone Breccia of the University of Pavia warned that the deployment marked “another step towards world war.”

Indicators escalate

Despite the backlash, the timing looks fortuitous for Russian President Vladimir Putin.

European and U.S. diplomatic and military assets are focused heavily on preventing a new Middle East war, while political leadership in the U.S. and elsewhere are consumed with domestic matters and upcoming votes.

The United States is preoccupied by a close, divisive presidential race, in the run-up to Nov. 6.  Japanese elect a new parliament on Oct. 27, though that election is predicted to be neither close, nor especially divisive.

Indications of North Korean troop movements to Russia are increasing.

South Korean intelligence on Friday released satellite images and said 1,500 special forces had already been sent to Vladivostok. Two film clips shot in Russia’s Far East have leaked online.

In one, supplied by Kyiv, Asian troops are seen in a depot, receiving uniform items. CNN posted a related document detailing clothes sizes in Russian and Korean.

In another, armed Asian troops in combat gear are seen on a training ground. Russian voices can be heard, speaking of larger numbers soon to arrive.

A leaflet is circulating on Russian social media, featuring an image of a North Korean soldier, and Korean translations of how to order Ukrainians to surrender. Unconfirmed images also show the North Korean flag on arm patches.

North Koreans would add greater weight to odds already swinging against Kiev.

Russia has been steadily advancing across eastern and southeastern Ukraine since seizing Bakhmut in June 2023. 

Ukraine’s August incursion into Russia’s Kursk Oblast won ground but failed to stem the tide. The Kursk incursion — where some believe North Korean troops may deploy — is itself under heavy pressure.

If used en masse, 12,000 highly trained troops — every North Korean male serves 10 years — could generate a decisive breakthrough, reckons Yang Uk, a security analyst at Seoul’s Asan Institute. He believes Pyongyang is deploying a heavy infantry division of three brigades, plus a light infantry brigade of special forces.

“Russian uses disposable units to attack, then heavy weapons take out Ukrainian defenses, before assault troops – airborne, or naval infantry – breakthrough, and line units follow up,” Mr. Yang said. “These tactics will apply to the North Koreans.”

However, North Korea has zero experience of overseas warfare beyond the company, or 120-man, level.

“East coming to West, rather than West going East, is new,” said Robert Collins, a civilian specialist who advises U.S. officers on North Korean affairs. “North Koreans ranked colonel and above have no experience on Western battlefields.”

Though U.S. and South Korean troops have been training jointly for more than 70 years, he said, language barriers still pose difficulties. For North Koreans and Russians, the interoperability problems will be magnified.

“I think they are going to end up being easy targets,” he said. “If 10,000 North Koreans fail miserably, is Kim Jong-un going to send 10,000 more? That’s problematic.”

How to respond

With donor nations fretting even over Kyiv’s use of long-range weapons, the U.S. and Ukraine’s other backers have to re-think their approach, Mr. Yang stated.

“Global democracies are really afraid of World War III,” said Mr. Yang. “But compare the manufacturing capacity of global democracies: We can out-produce Russia and North Korea.”

As well as accelerating arms shipments, Ukraine’s allies could directly deploy long-range, unmanned weapons in Ukraine, guided from nations such has Germany, South Korea, the U.K. and the U.S., he suggested.

While North Korea massively arms Russia, South Korea, a defense manufacturing powerhouse, declines to directly arm Ukraine. That policy may face new pressure in light of recent events.

“We’ll be fanning those flames,” vowed a Western officer in Seoul, speaking anonymously.

Jeff Roberson, who teaches diplomatic relations at Seoul’s Yonsei University, cautioned that the reports of North Korean aid and troops to Russia should be closely examined. Kyiv, he noted, has every reason to talk up threats – particularly from countries as toxic as Pyongyang.

“A lot of information regarding boots on ground, and on numbers, is coming from Ukrainian sources,” Mr. Robertson said. “There are lots of things North Koreans can be doing in Russia, including construction work and filling in roles that allow more Russians to go to the front.”