Russian troops appear close to driving Ukraine from all the territory it seized in the Kursk region of Russia last year, a battlefield success that would deny President Volodymyr Zelensky of Ukraine a significant bargaining chip in any negotiations.
The Russian push in Kursk appeared to accelerate after President Trump froze military aid and intelligence support to Ukraine on March 3. The flow of aid resumed this week as Ukraine agreed to a Trump administration proposal for a 30-day cease-fire with Russia.
On Thursday, Mr. Putin expressed preliminary support for the proposal but said he still had questions that required more discussion. Those questions, he told a news conference, included the fate of Ukrainian troops still in Kursk — suggesting that he may demand Kyiv order them to lay down their arms.
Here is a look at the Ukrainian incursion — the first on Russian soil since World War II — and how Russian troops are fighting back.
Why is Kursk important?
Kursk is an area of western Russia that borders the Sumy region of Ukraine. Sumy had long been thought to be a place where Russia might try opening a new front in its full-scale invasion of Ukraine, which began in February 2022.
But in a move that surprised even its key allies, Ukrainian troops caught Moscow off guard last summer, pouring across a thinly defended border and opening a new front themselves.
The main objectives, one Ukrainian colonel told The New York Times, were to divert Russian troops from the grueling fighting in the eastern Donbas region of Ukraine, push Moscow’s artillery out of range of the Sumy region and damage Russian morale.
Within weeks of the incursion, Ukraine had established control over a slice of Kursk that its officials said encompassed nearly 500 square miles of farmland and settlements. Though barely a sliver of Russia, the largest country in the world, the assault was an embarrassment for President Vladimir V. Putin. It also surprised Ukraine’s allies, including the United States, who had not been told in advance.
The most important town in Kursk that Ukrainian forces seized was Sudzha, an administrative center with a population of around 5,000 people before the incursion.
Analysts said that Ukraine’s offensive was a gamble, stretching its military resources at a time when Kyiv’s troops were struggling to defend a long front line in their own territory.
President Volodymyr Zelensky of Ukraine said that his military did not want to stay on Russian soil indefinitely, and that territory gained in Kursk could be used to strengthen Ukraine’s position in future negotiations with Moscow.
How has Russia responded?
Initially, rather than diverting large numbers of troops to defend Kursk, Mr. Putin said that eastern Ukraine remained Moscow’s main military focus. Russian troops continued their creeping advance within Ukraine, taking the town of Vuhledar in October and then pushing farther west.
Weeks into its incursion in Kursk, Ukraine’s push slowed and its troops began gradually to lose ground as Russian forces deployed there in greater numbers.
Then, in the fall, Russia received a boost from its ally North Korea, which deployed around 11,000 soldiers to Kursk to assist Moscow’s defense. The deployment at first unnerved Ukraine and its allies. But the North Korean troops suffered wave after wave of heavy losses and, for a time, were withdrawn from the frontline.
In recent weeks, Russian forces, assisted by North Korean fighters, have advanced rapidly in Kursk, using drones and fighter jets to retake much of the territory that Ukraine had held.
In a sign of renewed military confidence, Mr. Putin visited a command post near the front in Kursk late Wednesday, the Kremlin said.
Ukraine’s top military commander, Gen. Oleksandr Syrsky, pushed back against the idea of an immediate Ukrainian withdrawal from the area. He said on Wednesday night that Ukrainian troops would “hold the line in the Kursk region for as long as it remains reasonable and necessary.”
On Thursday, Russia’s Defense Ministry claimed that its forces had retaken Sudzha. There was no immediate comment from Ukraine. If confirmed, that Russian advance would leave only small pockets of Russian land along the border under Ukrainian control.