Satellite images show North Korea boosting arms flow to Russia

North Korea and Russia are deepening their military cooperation, as Pyongyang ramps up the supply of arms to Moscow for the war in Ukraine and receives much needed cash and oil from the Kremlin in return.

Recent satellite images show that North Korea is shipping more munitions to Russia and is expanding arms production at home to churn out the weapons Moscow needs to feed its voracious war machine. Assistance from North Korea is allowing Russia to press its advantage against exhausted Ukrainian troops and could help it resist pressure from the incoming administration of President-elect Donald Trump to end the conflict.

In turn, Pyongyang is already receiving much-needed cash and oil from Russia. Western officials worry North Korea could also ask for sensitive nuclear technology and material support from Russia in case of a war on the Korean Peninsula.

The deepening alliance between Russia and North Korea is alarming to the U.S. and its allies, making both countries more dangerous to their neighbors and more difficult to contain.

Millions of artillery shells from Pyongyang have allowed Russia to fill an ammunition deficit caused by almost three years of intense fighting. North Korean rockets are bombarding Ukrainian cities while Russia’s own missile production has been hobbled by Western sanctions. Military hardware, including multiple launch rocket systems, is flowing into Russia by train, with railroad traffic through the countries’ border reaching record highs.

Andriy Kovalenko, a Ukrainian army officer heading a government unit tasked with countering Russian disinformation, said 60% of the artillery and mortar shells used by Russia in Ukraine now come from Pyongyang. “North Korean ammunition is holding the Russian defenses,” he said.

North Korea’s missiles now make up nearly a third of Russia’s ballistic missile launches at Ukraine this year, according to Ukrainian officials.

Manpower has further helped Russia swing the balance. The roughly 12,000 soldiers dispatched from North Korea are now engaged in active combat, U.S. officials said on Monday. More than 100 have been killed and around a thousand injured in combat against Ukrainian units occupying parts of Russia’s Kursk region, South Korea’s spy agency told lawmakers in a closed-door meeting on Thursday.

North Korea has shipped some 20,000 containers of munitions to Russia, according to Washington and Seoul officials, ranging from lower-quality ammunition such as 122 mm and 152 mm artillery shells to its newer Hwasong-11 class ballistic missiles. Ukrainian officials say the provision has amounted to more than five million artillery shells and dozens of rockets, including more than 100 Hwasong-11 class missiles.

“They can be imprecise, but the range is impressive,” a senior Ukrainian intelligence official said of the North Korean missiles provided to Russia. “It’s a threat to our cities.”

More recently, Pyongyang has sent 170 mm self-propelled howitzers and 240 mm long-range multiple rocket launchers.

The artillery shells initially supplied by North Korea were decades-old, raising suspicions that the Kim regime was dumping its old ammunition. But now, Pyongyang is supplying newer munitions. For instance, the 240 mm multiple rocket launchers sent to Russia were recently equipped with new guidance and control systems.

Similarly, North Korea’s largest 600 mm rocket launchers, or KN-25, were upgraded earlier this year with the support of Russian technicians, according to SI Analytics, a satellite imagery firm. The weapon, first tested in 2019, blurs the distinction between a multiple launch rocket system and a short-range ballistic missile.

More weapons are coming, by ship and train, to resupply Russian troops burning through huge quantities of arms, U.S. and South Korean officials say. Around 200 munitions factories in North Korea are operating at full capacity to produce weapons, and Russia is transferring fuel and equipment to support Pyongyang’s arms manufacturing, Seoul officials said.

A missile manufacturing complex producing the North Korean short-range ballistic missiles fired at Ukraine is expanding as well, according to satellite imagery. North Korea’s Hwasong-11 class missiles, dubbed KN-23 and KN-24 in the West, are produced at a plant on North Korea’s eastern coast. New construction appeared to be progressing rapidly, including a new building apparently aimed at concealing loading operations of the factory, SI Analytics said. Kim has visited the factory several times, during which he ordered the mass production of tactical missiles.

North Korean factories are capable of producing new Hwasong missiles in just months, said Damien Spleeters, the director of expeditionary operations at Conflict Armament Research. “The North Korean missiles are being made on demand,” he said.

At a defense expo last month, North Korea featured eight different types of drones. Some weapons experts say North Korea appears to be making improvements to Russian drones that would then be exported back to Russia to replace rapidly depleting stocks.

“North Korea continues to showcase its munitions-production capabilities, and Russian technical support will accelerate its exports,” said Hong Min, a senior researcher on North Korea at the Korea Institute for National Unification, a state-funded think tank in Seoul.

Russian Telegram channels have been posting clips of North Korean howitzers trundling along railcars in Russia. Railroad traffic reached record highs this year at the Tumangang-Khasan crossing at the Russia-North Korea border, with the number of railcars tripling this year since a meeting between Kim and Russian President Vladimir Putin last September.

Neither the Kremlin nor the Russian Defense Ministry responded to requests for comment. In November, North Korea’s foreign minister said Pyongyang would stand by Moscow’s side “until the day of victory.”

The cooperation goes both ways. Moscow is transferring air defense systems and sending technicians to support North Korea’s spy satellite efforts, Seoul officials said. Pyongyang’s outdated air defense system needs significant improvements to match Seoul and Washington’s superior air forces, weapons experts say. South Korean officials said North Korea is likely also seeking help from Russia on intercontinental ballistic missile technology.

North Korea has also received more than a million barrels of oil since March, twice the annual cap imposed under United Nations sanctions, according to the London-based Open Source Centre.

The arms deals with Russia could have earned up to $5.5 billion for North Korea since the start of the war in Ukraine, according to Olena Guseinova, a researcher at the Hankuk University of Foreign Studies in Seoul, who analyzed intelligence reports, leaked documents and ammunition prices from previous North Korean arms deals. Russia could pay Pyongyang up to $572 million annually for the troops North Korea has supplied. That is more than double the peak trade between Russia and North Korea, which reached around $233 million in 2005, Guseinova estimated.

When the North Korean soldiers initially deployed to the Kursk region in the fall, they focused on observing the Russians and learning how to use electronic-warfare systems and deploy drones in guiding artillery and mortar strikes on enemy positions, a Ukrainian intelligence official said.

But since the North Korean soldiers have been deployed to fight, Ukrainian officials say Russia is seeking to conceal their involvement in combat, removing dead and wounded from the battlefield even as Russian bodies are often left behind. The wounded North Koreans are transported in trains to Russian hospitals far from the front, where they are kept apart from Russian soldiers, the Ukrainians say.

The effort to conceal the identities of North Korean casualties could be an attempt to hide Pyongyang’s troop deployment from the international community, given that neither Russia nor North Korea have officially acknowledged the move. Seoul officials said the North Korean soldiers were given fake identities upon arriving in Russia.

North Korea has denied supplying arms to Russia on multiple occasions. In October, a North Korean representative dismissed its troop deployment as “groundless rumors” at the U.N. General Assembly.

On Wednesday, Ukraine’s SBU intelligence service posted audio of what it said was an intercepted phone call in which a Russian nurse says more than 200 wounded North Koreans are being treated at her hospital near Moscow, where whole sections have been set aside for them. Russian translators are struggling to mediate between the troops and the hospital staff, she says.

“A train came in yesterday, around 100 people, today 120 more, that’s 200. God only knows how many more are there” in the Kursk region, the woman said in a conversation with her husband, according to the SBU. The Wall Street Journal wasn’t able to verify the conversation.

Kate Vtorygina contributed to this article.

Write to Dasl Yoon at dasl.yoon@wsj.com and Matthew Luxmoore at matthew.luxmoore@wsj.com