Fears grew today for hundreds of Ukrainians trapped in a factory in stricken Severodonetsk.
Defiant Kyiv ignored Moscow’s surrender demands as Russia continued to attack with rockets, mortars and machine guns.
More than 500 civilians, including 40 children, are stranded at the Azot chemical plant.
If the ruined city falls, President Vladimir Putin will celebrate the capture of Luhansk, one of two contested Donbas regions.
Severodonetsk has for weeks been the main focal point of the war and more than 1,000 Ukrainian troops are defending the position.
Mayor Oleksandr Stryuk said: “We are trying to push the enemy towards the city centre... this is an ongoing situation with partial successes and tactical retreats. The escape routes are dangerous, but there are some.”
The Azot bombardment echoes the siege of the Azovstal steelworks in the southern port of Mariupol, which fell to Putin’s forces last month.
Moscow claims Donbas on behalf of separatists and re-focused its assault there after failing to take Ukraine 's capital.
US Defence Secretary Lloyd Austin told fellow NATO defence ministers in Brussels the invasion was at a “pivotal moment”.
He added: “We can’t afford to let up and we can’t lose steam. The stakes are high.”
Demanding more weapons from the ministers, President Volodymyr Zelensky said: “We have to hold strong.”
Kyiv is losing 100 to 200 soldiers a day, while Russia is said to have lost 31,000 since the February 31 invasion.
Moscow recently lost its 53rd and 54th colonels in the conflict, it was revealed.
Sergei Postnov, in his 40s, died this week in Luhansk and paratrooper Sergei Krasnikov, 56, was killed in Ternove in the Kharkiv region.
