Ukrainian forces went 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.

The Russian Ministry of Defense said Ukrainian forces launched a large assault featuring tanks, mine-clearing equipment and at least a dozen armored vehicles, and it claimed to have thwarted the attack. After Ukrainian forces unexpectedly attacked Kursk last summer, they took about 500 square miles of territory that Russia has been slowly clawing back.

Andrii Kovalenko, a senior Ukrainian government official focused on Russian disinformation operations, issued a statement referring to the Kursk region, saying that “the Russians are very worried because they were attacked on several fronts and it was a surprise for them.”

Ukrainian soldiers fighting in the area who were reached by phone declined to discuss ongoing operations beyond saying that Ukraine was on the offensive in parts of the Kursk region and that fierce fighting was raging there.

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

Military analysts said that the attacks could be a deliberate attempt at misdirection, forcing Russian forces to react to one part of the front in the hopes of weakening them elsewhere.