Ukraine said it was strengthening its forces around Bakhmut in the eastern Donbas region and repelling constant attacks there by the Russian mercenary group Wagner, whose leader has vowed to capture the area's vast underground mines.
Kyiv had sent reinforcements to Soledar, a small town near Bakhmut where the situation was particularly difficult, Ukrainian officials said.
"The enemy again made a desperate attempt to storm the city of Soledar from different directions and threw the most professional units of the Wagnerites into battle," Ukraine's military said in a statement.
Yevgeny Prigozhin, the founder of the Wagner mercenary group, has been trying to capture Bakhmut and Soledar for months at the cost of many lives on both sides. He said on Saturday its significance lay in the network of mines there.
"It not only (has the ability to hold) a big group of people at a depth of 80-100 metres, but tanks and infantry fighting vehicles can also move about."
Military analysts say the strategic military benefit for Moscow would be limited. A US official has said Prigozhin, a powerful ally of Russian President Vladimir Putin, is eyeing the salt and gypsum from the mines.
President Volodymyr Zelenskyy said in nightly video remarks on Sunday that Bakhmut and Soledar were holding on despite widespread destruction after months of attacks.
"Our soldiers are repelling constant Russian attempts to advance," he said. In Soledar "things are very difficult".
Pro-Russian bloggers quoted Prigozhin as saying his forces were fighting for the administration building in Soledar.
The Ukrainian military said reinforcements had been sent to Soledar, and everything was being done to fend off the enemy.
"There are brutal and bloody battles there -- 106
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