Ukraine Attacks Kursk Region of Russia Anew

Ukrainian forces have gone on the offensive in the Kursk region of Russia, Ukrainian and Russian officials said Sunday, in what appeared to be an effort to regain the initiative there as they struggle to thwart relentless Russian assaults across eastern Ukraine.

Ukraine took about 500 square miles last summer in the Kursk region in a surprise incursion, but Russia clawed back about half of the territory in the months that followed.

On Sunday, the Russian Defense Ministry said Ukrainian forces had launched a large new assault featuring tanks, mine-clearing equipment and at least a dozen armored vehicles. The ministry claimed to have thwarted the attack.

Ukrainian soldiers fighting in the area who were reached by phone declined to discuss continuing operations beyond saying that Ukraine was on the offensive in parts of the Kursk region and that fierce fighting was raging there. The Ukrainian military high command said on Sunday night that there were 42 “combat engagements” in the region over the past 24 hours and that 12 were still happening.

It was not possible to verify the claims by either side independently, and the scope of the Ukrainian assaults remained unclear.

Ukrainian and Western military analysts said that the attacks could be a deliberate attempt at misdirection, trying to force Russian troops to shore up defenses there in the hopes of weakening them on the front line in Ukrainian territory.

Russian forces continue to make costly but consistent gains in the Donetsk region in eastern Ukraine. They are steadily grinding down a pocket of resistance around the town of Kurakhove and are also fighting to envelop the larger nearby city of Pokrovsk, Ukrainian soldiers and officials said.

Russian troops are now within one mile of a critical supply road leading to Pokrovsk, which had served as a vital logistics and transportation hub for Ukrainian forces in the region.

Some American officials initially expressed skepticism about the wisdom of Ukraine’s incursion into Russia’s Kursk region last August, concerned that it might be a drain on already exhausted and undermanned brigades struggling to stabilize defensive lines in eastern Ukraine.

But as Russian casualties mounted, some of those American officials changed their assessments.

Although Ukraine now holds less than half of the territory it seized in the Kursk offensive last summer, it has managed in recent weeks to slow Russia’s advances despite repeated waves of Russian counterattacks, including assaults bolstered by thousands of North Korean soldiers.

President Vladimir V. Putin of Russia has sought to play down the significance of the Kursk incursion, which was the first ground invasion of Russia since the end of World War II.

While saying that it was the military’s “sacred duty” to expel Ukrainian forces, he recently declined to offer a timeline for when that might be accomplished.

“We will definitely drive them out,” Mr. Putin said at his annual news conference in December. “I cannot answer the question about a specific date right now.”

The Ukrainian president, Volodymyr Zelensky, said Moscow continued to pay a high price trying to push the Ukrainians out.

“Specifically, in battles today and yesterday near just one village — Makhnovka in the Kursk region — the Russian army lost up to a battalion of infantry, including North Korean soldiers and Russian paratroopers,” Mr. Zelensky said on Saturday night. A battalion is composed of 600 to 800 soldiers.

It was not possible to verify his claim, but the Pentagon recently said that North Korea was suffering mass casualties on the Kursk front, with more than 1,000 killed or wounded in only a few weeks.

RIA Novosti, a Russian state news agency, said that about 340 Ukrainian soldiers had been killed and wounded in Kursk the past 24 hours. That claim also could not be independently verified, and the news agency, citing the Russian Defense Ministry, did not mention Russian casualties.

Mr. Zelensky said that holding on to land in Kursk gave Kyiv a “very strong trump card” in any possible negotiations with Moscow.

President-elect Donald J. Trump has vowed to end the war rapidly once he takes office, without saying how.

Liubov Sholudko, Nataliia Novosolova and Valerie Hopkins contributed reporting.