Intense fighting between Russian and Ukrainian forces has taken place around two towns in the Donetsk region of eastern Ukraine, Bakhmut and Soledar.
"The key hot spots in Donbas are Soledar and Bakhmut," Ukraine's President Volodymyr Zelenskyy said in his nightly video address.
"Very heavy fighting is going on there," he said.
The town of Bakhmut has been the next target of Russia's armed forces in their slow advance through the Donetsk region since taking the key industrial towns of Lysychansk and Sievierodonetsk in June and July.
Soledar lies just to the north of Bakhmut.
Fighting has been particularly intense this weekend in the Donetsk and Luhansk regions, which make up the larger industrial Donbas and the strategically important Kherson province in the south.
They constitute three of the four provinces Russian President Putin proclaimed as part of Russia last month, moves dismissed by Ukraine and its Western allies as illegitimate.
Russian forces shelled Ukrainian positions on several fronts on Sunday, the General Staff of Ukraine's Armed Forces said, with the targets including towns in Kharkiv, Donetsk and Kherson regions.
Shelling by Ukrainian forces damaged the administration building in the city Donetsk, capital of the Donetsk region, the head of its Russian-backed administration said on Sunday.
There was no immediate reaction from Ukraine to the attack on Donetsk city, which was annexed by Russian-backed separatists in 2014 along with swathes of the Donbas.
The Moscow-aligned Donetsk People's Republic has been in charge of the city of Donetsk since 2014 and among its prized strongholds in the Mayoral administration block.
The direct Ukrainian strike destroyed its roofing, structural supports and the car park outside.
No deaths were reported in the attack, but dozens have been in the wider Donetsk region where Russia's lines are holding against fierce bombardment.
Russia sends troops to Belarus
Thousands of Russian troops have been sent to Belarus, further raising tensions along Ukraine's north-western border.
Russia's defence ministry announced troop trains have already transported personnel into Belarus.
In total, just under 9,000 Russians are set to be based in the country.
Belarus's President Alexandr Lukashenko, who is an avowed supporter of Vladimir Putin, claimed his country's borders are being threatened by Ukraine to its south.
Earlier, Mr Lukashenko announced some of his troops would form a joint military group with Russia, without specifying where.
He said the two countries would be linking up in response to what he claimed was a clear threat to Belarus from Kyiv and its backers in the West.
Hosting Russian troops would raise the risk of conflict, but most Western analysts view the likelihood of a second front for full-blown war along Ukraine's northern border as remote.
Gunmen kill 11 at Russian army base
Russia opened a criminal investigation after gunmen shot dead 11 people at a military training ground near the Ukrainian border authorities said on Sunday.
Russia's RIA news agency, citing the defence ministry, said two gunmen opened fire with small arms during a firearms training exercise on Saturday, targeting personnel who had volunteered to fight in Ukraine. RIA said the gunmen, who it referred to as "terrorists", were shot dead.
The incident in the south-western Belgorod region was the latest blow to Mr Putin's "special military operation" in Ukraine.
It came a week after a blast damaged a bridge linking mainland Russia to Crimea, the peninsula it annexed from Ukraine in 2014.
Russia's defence ministry said the attackers were from a former Soviet republic, without elaborating.
A senior Ukrainian official, Oleksiy Arestovych, said the two men were from the mainly Muslim Central Asian republic of Tajikistan and had opened fire on the others after an argument over religion.
Reuters/ABC
