A Russian-installed official in the Russian-controlled part of Ukraine's Kharkiv region said on Friday that Ukrainian forces had registered a "substantial victory" by breaking through Russian defenses in the region.

Ukrainian President Volodymyr Zelenskiy said Thursday that Ukrainian troops had "liberated dozens of settlements" and reclaimed more than 1,000 sq km (400 sq miles) of territory from Russian forces in the east and south in the past week.

Speaking to Russian state television on Friday, Vitaly Ganchev said: "The very fact of a breach of our defenses is already a substantial victory for the Ukrainian armed forces."

Russia's defense ministry posted video footage of what it said were Russian troops being sent to the Kharkiv region.

Parts of Ukraine east of Kharkiv, Ukraine's second city, have been under Russian control since shortly after the Kremlin ordered its armed forces into Ukraine on Feb. 24, although Russia has been unable to take the city itself.

Zelenskiy had posted a video in which Ukrainian soldiers said they had captured the town of Balakliia, which lies along part of the frontline south of Kharkiv. It was the first rapid advance of its kind reported by either side for months.

The Kremlin declined to comment on reports of a Ukrainian advance in the Kharkiv region, referring questions to the Russian Defense Ministry.