Five months after Ukrainian forces swept across the border in the first ground invasion of Russia since World War II, the two armies are engaged in some of the most furious clashes of the war there, fighting over land and leverage in the conflict.
The intensity of the battles recalls some of the worst sieges of eastern Ukraine over the past three years, including in towns like Bakhmut and Avdiivka, names that now evoke memories of mass slaughter for soldiers on both sides.
The fighting, in the Kursk region of Russia, has taken on a layer of significance for the territory’s potential to play a role in any cease-fire negotiations. Facing the prospect of an unpredictable new U.S. president — who has vowed to end the war swiftly, without clarifying the terms — Ukraine hopes to use Russian territory as a bargaining chip.
Russia, relying on North Korean reinforcements, hopes to knock that territory out of Ukraine’s grasp.
“Here, the Russians need to take this territory at any cost, and are pouring all their strength into it, while we are giving everything we have to hold it,” said Sgt. Oleksandr, 46, a leader of a Ukrainian infantry platoon. “We’re holding on, destroying, destroying, destroying — so much that it’s hard to even comprehend.”
He and other soldiers, asking to be identified by only a first name or call sign in accordance with military protocol, said that attacking North Korean infantry had made the battles far more ferocious than before.
“The situation worsened significantly when the North Koreans started arriving,” said Jr. Sgt. Oleksii, 30, a platoon leader. “They are pressuring our fronts en masse, finding weak points and breaking through them.”
Russia, with the help of an estimated 12,000 North Koreans, has retaken about half of the territory it lost over the summer. Its assaults over the past week have further eaten into the territory held by Ukraine.
But Ukrainian forces have also gone on the attack in recent days, seeking to secure an area west of Sudzha, a small town in Russia about six miles from the border that has become the anchor for Ukrainian forces, which seized about 200 square miles in August.
“If they keep pressing us and we don’t push back, the enemy will feel a sense of superiority,” said Andrii, 44, a military intelligence officer. “When someone keeps hitting you, and you don’t hit back, the attacker will feel psychologically comfortable, even relaxed.”
The Russians have largely thwarted the assault, but fighting goes on and the situation remains unpredictable, soldiers said.
The intensity of the battles could be glimpsed on the road approaching the Russian border: A steady stream of tanks, armored personnel carriers and other vehicles rolled past broken down and blown-up equipment.
Russian bombs and rockets exploded with thunderous force in border villages, and Ukrainian missiles could be seen streaking across the sky in the opposite direction.
Tens of thousands of drones hunted targets, too. They have transformed the battlefield, although Ukraine has improved its electronic warfare abilities, limiting the effectiveness of drones that rely on radio signals. Russia has now flooded the theater with drones guided by ultrathin fiber-optic cables, with a flying range of more than 10 miles.
The best current defense against them is a shotgun, Ukrainian soldiers said.
The renewed fighting comes against a deeply uncertain political backdrop. The U.S. president-elect, Donald J. Trump, spent months on the campaign trail questioning American military assistance to Ukraine. He has said he wants to bring the war to a swift end, but has not indicated how.
Russian forces have been on the offensive for more than a year in eastern Ukraine, making steady advances despite staggering losses.
With its incursion, Ukraine aims to create a buffer zone to protect hundreds of thousands of civilians in the city of Sumy, less than 20 miles from the border with Russia. Ukraine also wants to ease pressure on the eastern front by drawing Russians back onto their own land.
President Volodymyr Zelensky said the campaign had sent a powerful message to the world that Ukraine can do more than play defense.
“It’s one of our wins, I think one of the biggest wins, not just last year, but throughout the war,” Mr. Zelensky said on Thursday in Germany, while meeting representatives of nations providing military support to Ukraine.
Still, some military analysts have cautioned that Ukraine’s Kursk campaign could leave its forces increasingly stretched and losing ground in its own eastern Donbas region.
Many soldiers fighting in Kursk believe that the painful losses in eastern Ukraine would have been even worse without their campaign.
“We have to understand the Russians use their most elite soldiers and best reserves in this area,” said Capt. Oleksandr Shyrshyn, 30, a battalion commander in the 47th Mechanized Brigade. “Considering what they could be doing in other parts of Ukraine, it is good.”
He was still bleary-eyed after a battle, a few days earlier, to thwart a large Russian assault.
The Russians attacked Ukrainian positions in six waves, employing more than 50 tanks, armored personnel carriers and other vehicles.
While dozens of enemy soldiers were killed and injured and a large amount of the Russian equipment destroyed, Captain Shyrshyn said, the Russians advanced a couple of miles.
“When the first wave comes, we focus on it, deal with it, and then the next one comes,” he said. There is no time to redirect artillery or other resources as the next wave moves in from a different line of attack.
“We fall behind,” he said. “Then the next wave comes, and one of them manages to reach the required section and accomplish its task.”
It remains difficult, he said, to see how so many in the West view the war in Ukraine like a video game and refuse to see the threat Russia poses to the world.
He acknowledged the decline in Ukrainian morale over nearly three years of war, but said most soldiers still understood why they must fight. “Stopping will mean our death, that’s all,” he said.
North Korea’s entry into the war, some Ukrainian soldiers said, should alarm European nations and their allies.
The North Korean troops have fought as a disciplined, dedicated and fearless force, they said, typically moving in large formations on foot, even through minefields while under heavy artillery fire and being stalked by drones. The Ukrainian authorities on Saturday said that their forces captured two North Korean soldiers and that they were the first to be taken alive so far.
Sgt. Oleksandr, the platoon leader, said the carnage in Kursk was as terrifying as anything he had witnessed since joining the army in 2014.
“You look and can’t fully grasp where you are, seeing every day how many people we destroy,” he said.
He compared it with Bakhmut, when machine gunners had to be regularly replaced because they could not handle the pace of killing. “After two hours of laying down so many people, they couldn’t take it mentally,” he said.
“It’s the same here now,” he said, sharing a cellphone video showing the aftermath of a recent assault. The field was littered with bodies, torn and twisted and piled in ways that made it hard to count the dead.
“The worst is for the infantry,” he said. “When you’re sitting there, and they’re coming at you, and everything is flying at you.”
Anastasia Kuznietsova contributed reporting.
