Russia's military said Monday it had repelled "a large-scale offensive" by Ukrainian forces in Moscow-annexed Donetsk.
Kyiv has for months said it is preparing a major counteroffensive, hoping to reclaim territory lost since Russia launched its military operation in February 2022.
Russia's Ministry of Defence reported that on Sunday, in the south of the region, "the enemy launched a large-scale offensive in five sectors of the front".
"A total of six mechanised and two tank battalions of the enemy were involved," it said in a Telegram post, adding that Ukrainian troops had hit "the most vulnerable, in their opinion, sector of the front".
"The enemy did not achieve their tasks, they had no success."
The ministry posted what it said was a video of the battle, showing Ukrainian armoured vehicles coming under heavy fire.
The conflict, which has dragged on for more than 15 months, escalated this week with increased attacks on both sides of the border.
The same day, the governor of Russia's Belgorod region on the border with Ukraine said fighting was ongoing on his side of the frontier and acknowledged that pro-Ukrainian forces had taken Russians prisoner during cross-border clashes.