North Korean soldiers fighting for Moscow in Russia’s Kursk region have been given their own pieces of land to attack. Unlike their Russian counterparts, they advance almost without armored vehicles in support.

When they attack, they don’t pause to regroup or retreat, as the Russians often do when they start taking heavy casualties, Ukrainian soldiers and U.S. officials say. Instead, they move under heavy fire across mine-strewn fields and will send a wave of 40 or more troops.

If they take a position, they don’t try to secure it. They leave it to the Russian reinforcements, and they retreat and prepare for a new attack.

They also developed special tactics and habits. When fighting a drone, the North Koreans send one soldier as a decoy so that the others can shoot it down. If seriously wounded, they were instructed to detonate a grenade to avoid being captured alive, holding it under their neck with one hand on a pin as Ukrainian soldiers approached.

Sent to Russia to join Moscow’s troops in Kursk, the North Koreans are essentially operating as a separate fighting force, Ukrainian soldiers and U.S. officials said — different in language, training and military culture.

“It’s partly two different militaries that have never trained or operated together, and partly, I think, it’s the Russian military culture, which, so to speak, doesn’t have a lot of respect for the capabilities and norms and operations of partner forces,” said Celeste A. Wallander, who until the day of the inauguration was the assistant secretary of the Pentagon for international security issues.

The North Koreans are mostly special operations troops trained for surgical strike missions, she said, but the Russians basically used them as foot soldiers.

Last fall, North Korea sent about 11,000 troops to help Moscow’s forces in the Kursk region of southern Russia, where the Ukrainians seized the territory in a surprise invasion last summer. Since their first combat engagement in early December, roughly one-third of North Korean soldiers have been killed or wounded, Ukrainian and U.S. officials said.

General Oleksandr Syrsky, Ukraine’s top military commander, said this week that North Korean casualties continued to mount, estimating that almost half of those sent were either injured or killed, but warned that they were “highly motivated, well trained” and “ brave.”

The reinforcements are expected “within the next two months,” according to a senior US defense official.

The New York Times spoke with a dozen Ukrainian soldiers and commanders engaged in direct combat with North Korean soldiers, as well as four US defense officials and military analysts, to paint a portrait of how the North Koreans operate on the battlefield. The Times also viewed video of the North Korean attacks provided by the Ukrainian military.

U.S. officials requested anonymity to speak candidly about battlefield details. The Ukrainian soldiers and their commanders asked to be identified only by name in accordance with military protocol.

With 1.2 million troops, North Korea’s military is among the largest standing armies in the world, and its entry into the war was a major escalation in a war now approaching its fourth year.

Even before it sent troops to Russia, North Korea was a major supporter of the Russian war effort. It has sent Moscow millions of artillery shells – which now account for about half of Russia’s ammunition fired daily – and more than 100 short-range ballistic missiles, according to Western and Ukrainian intelligence officials.

Kremlin denied deployment North Korean soldiers on the battlefield and are taking steps to hide their involvement, officials said.

For example, North Koreans have been issued what one Pentagon official described as “pocket junk” – documents registering them as being from the Russian Far East.

President Volodymyr Zelensky said that one of the captured soldiers had a military ID in the name of a resident of Tuva, in southern Siberia. The fake identity used the information of a real Russian citizen, Ukrainian intelligence officials said.

Ukrainian claims of attempts to cover up North Korean involvement could not be independently verified.

As North Korean soldiers provide additional manpower, the Russians struggle to integrate them into the battlefield.

Difficulties have ranged from minor issues, such as finding uniforms small enough to fit North Korean soldiers, to communication problems that have led to direct confrontation between North Korean and Russian forces at least twice over mistaken identity, U.S. officials and Ukrainian soldiers said.

The Russians are taking steps to address the problem, Ukrainian soldiers said, but have yet to form a more cohesive fighting force.

“Now they have started putting together groups that include a translator or someone who speaks Russian with a radio, but these groups are not very effective,” said Andrii, the Ukrainian commander.

Using video from a drone camera, Andrii described the attack shortly after it happened earlier this month, offering insight into North Korean tactics.

Seen through thermal imaging, the North Korean soldiers stood out as small dark spots on the snow-dusted fields. They walked some five miles – with many killed along the way – and assembled in a tree line for an attack on a Ukrainian trench not far from them.

“There are about 50 of them here,” Andrii said.

Some were wounded, the video shows, but they did not retreat. They waited for reinforcements and then attacked. Assault groups consisted of five to eight soldiers.

The North Koreans are taking many casualties, Andrii said, but continue to send in new units.

“Go ahead, go ahead,” he said. “It’s motivation, orders and strict discipline.”

The “shock brigade” tactic of soldiers advancing with little regard for the mess that awaits them features heavily in North Korean military training and propaganda. Adopted from the days of the Korean War, the strategy has caused many casualties in a war fought in open and flat areas with drones, according to South Korean intelligence officials. But they said the North would see those losses as a necessary cost to become more adept at modern warfare.

“It seems like they came here just to die, and they know it,” said Oleksii, the platoon commander.

Ukrainian intelligence officials said the two North Korean soldiers captured on Jan. 9 also provided insights into the deployment of forces in Kursk. Ukrainian special operations forces have released excerpts from numerous diaries and communications collected from the bodies of North Korean soldiers, which US officials have said appear to be authentic.

In one diary, a North Korean soldier wrote that he was motivated to join Russia’s fight to atone for an unspecified transgression.

“I wear the uniform of the revolution to protect the commander-in-chief,” he wrote. “I betrayed the Party that trusted me and committed ungrateful acts against the Commander-in-Chief. The sins I committed are unforgivable, but the homeland gave me a path of redemption, a new beginning in life.”

He also included practical details, such as shooting down a drone.

“At the same time, the one who lures the drone keeps a distance of 7 meters, while those who shoot remain 10-12 meters away. If the decoy is stationary, the drone will also stop moving. At this point the shooter eliminates the drone.”

North Korean tactics forced the Ukrainians to adapt.

For example, drone pilots said they generally did not target individual North Koreans, but hunted groups.

And given the density of North Korean attacks, the standard procedure of placing anti-personnel mines at a distance of about 15 meters does not work well. Now, the soldiers say, they try to leave no more than five meters between the mines.

It is interesting, Ukrainian soldiers said, that the North Koreans try to remove their dead and wounded from the battlefield, which is different from the Russians.

Andrii shared drone footage of the process, with some dead and wounded soldiers being dragged out — dragged by the arms or loaded onto sleds — while others were brought into position.

North Korean forces deployed in Ukraine included about 500 officers and at least three generals, according to Ukraine’s military intelligence service.

The generals are posted to Russia’s command and control headquarters, U.S. defense officials said, and that’s where targets are decided.

Commanders decide when they need artillery and how long to wait before maneuvering ground forces, a senior U.S. defense official said. They sync with troops on the ground, so troops don’t talk to their Russian counterparts, to try to reduce miscommunication.

Ukrainian soldiers fighting in Kursk said the North Korean tactic was costly but effective.

“The Koreans are starting to push the front lines, targeting less defended areas and thus exhausting our troops,” said Oleksii, the platoon commander.

Fighting one of the world’s largest armies was hard enough, he said, but fighting two was “on the edge” of what was possible.

Capturing the prisoners proved challenging because the North Koreans were trained not to be captured alive, the soldiers said, and Russian drone operators were always watching.

“If the Russians see that the Koreans are captured, they use drones to finish them off – killing both the Koreans and our soldiers,” Oleksii said, adding that some in his brigade had recently been killed this way.

Ukrainian soldiers said the North Koreans should not be underestimated.

“They’re being tested, they’re really being tested,” said Andrii, the drone’s commander. They had no combat experience, he said, but “now they are here, gaining it and becoming very strong.”

Ljubov Soludko contributed reporting from Ukraine and Choe Sang-Hun contributed from Seoul.