Russian forces have bombarded areas of Ukraine's eastern Donbas region from land and air, destroying houses in residential districts and killing civilians.
President Volodymyr Zelenskiy says the assaults have turned the Donbas into "hell".
As the war nears its three-month mark, the Ukrainian general staff say massive artillery barrages, including multiple rocket-launchers, have hit civilian infrastructure.
Russian aircraft have also struck at targets, the general staff said in a statement on Friday.
"The Russian army has started very intensive destruction of the town of Sievierodonetsk, the intensity of shelling doubled, they are shelling residential quarters, destroying house by house," Luhansk governor Serhiy Gaidai said via his Telegram channel.
"We do not know how many people died, because it is simply impossible to go through and look at every apartment."
Earlier reports had put the civilian death toll in the Luhansk area of the Donbas at 13 in the past day, with 12 of them in Sievierodonetsk, which lies on a river about 110 km northwest of the regional capital.
"The Donbas is completely destroyed," President Zelenskiy said in an address on Thursday night. "It is hell there - and that is not an exaggeration."
Reuters could not independently verify the reports and Russia denies targeting civilians.
In Moscow, Russian Defence Minister Sergei Shoigu said the "liberation of the Luhansk People's Republic" would be completed soon.
The industrial region compromises the Donetsk and Luhansk areas, parts of which are controlled by Moscow-backed separatists.
"Groupings of the Russian Armed Forces, together with units of the people's militia of the Lugansk (Luhansk) and Donetsk people's republics, continue to expand control over the territories of the Donbas," Shoigu said in a speech.
Russia's focus on the Donbas follows its failure to capture the capital Kyiv in the early stages of the invasion launched by Russian President Vladimir Putin on February 24.
In the weeks of warfare pitting Russia's military might against dogged Ukrainian resistance, thousands of people have been killed and whole towns and cities shattered in the gravest crisis in Europe in decades.
Almost a third of Ukraine's people have fled their homes, including more than six million who have left the country in a refugee exodus, while others remain trapped in cities pulverised by Russian bombardments.
British military intelligence said on Friday Russia is likely to further reinforce its operations in the Donbas once it finally secures the southern port city of Mariupol - scene of a weeks-long siege and Russia's most significant success in a campaign of mixed fortunes for the Kremlin.
In a sign of Russia's need to bolster its war effort, the parliament in Moscow said it would consider a bill to allow Russians over 40 and foreigners over 30 to sign up for the military.
Putin calls the invasion a "special military operation" to rid the country of fascists - an assertion Kyiv and its Western allies say is a baseless pretext for an unprovoked war.
The Kremlin leader was due to hold a security council meeting later on Friday.
Australian Associated Press
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