Russian and Russian-backed separatist forces in the Donetsk region of Ukraine have suffered heavy casualties, according to UK intelligence officials.
They estimate the Donetsk militia alone has lost 55% of its original force.
Russian forces are focused on conquering all of neighbouring Luhansk, aiming to encircle the city of Lysychansk, say Ukrainian leaders.
Regional chief Serhiy Haidai said there had been "colossal destruction" in the city.
He said the situation in its sister city of Severodonetsk was "hell", and quoted the mayor as saying some 7,000-8,000 civilians remained there.
UK military intelligence said Russia was very likely aiming to deploy a large number of reserve units to Ukraine's eastern Donbas, which is made up of Donetsk and Luhansk.
It drew attention to the "extraordinary attrition" suffered by Russian and Russian proxy forces in Donbas. While Russia has for months avoided detailing its casualties, the human rights ombudsman in the so-called Donetsk People's Republic said last week that 2,128 of its forces had been killed and 8,897 wounded. A further 654 civilians had been killed, said Daria Morozova,
Ukrainian President Volodymyr Zelensky said in his late-night address on Tuesday that while Luhansk was currently the toughest area, the invading army was also "putting serious pressure on the Donetsk direction".
https://www.bbc.co.uk/news/world-europe-61891462