Ukraine has ignored a Russian ultimatum to surrender the eastern city of Sievierodonetsk as the United States urged its allies at a gathering of NATO defence ministers to step up military support.
Sievierodonetsk, now largely in ruins, has for weeks been the main focal point of the war.
Russia had told Ukrainian forces holed up in a chemical plant there to stop “senseless resistance and lay down arms” from Wednesday morning, pressing its advantage in the battle for control of eastern Ukraine.
Ukraine says more than 500 civilians, including 40 children, remain alongside soldiers inside the Azot chemical factory, sheltering from weeks of almost constant Russian bombardment.
The mayor of Sievierodonetsk, Oleksandr Stryuk, said Russian forces were trying to storm the city from several directions but the Ukrainians continued to defend it and were not totally cut off, even though all its river bridges had been destroyed.
“The situation is difficult but stable,” he told Ukrainian television.
“The escape routes are dangerous but there are some.”
He made no reference to the Russian ultimatum.
Russia had said it would let civilians leave the plant on Wednesday but Russian-backed separatists said Ukrainian shelling had scuppered the plan, which would have involved taking people out towards territory they control.
Serhiy Gaidai, governor of the Luhansk region containing Sievierodonetsk, said Ukraine’s army continued to defend the city and to stop Russian forces from taking its twin city Lysychansk on the opposite bank of the Siverskyi Donets river.
“Nevertheless, the Russians are close and the population is suffering and homes are being destroyed,” he posted online just before Russia’s 8am Moscow time deadline.
Reuters could not immediately verify the battlefield accounts.
Luhansk is one of two eastern provinces Russia claims on behalf of separatist proxies.
Together they make up the Donbas, an industrial Ukrainian region where Russia has focused its assault.
Addressing dozens of NATO defence ministers meeting in Brussels to debate their next moves, US Defense Secretary Lloyd Austin said the invasion was at a “pivotal moment”.
“We can’t afford to let up and we can’t lose steam. The stakes are too high,” he said at the start of the talks.
NATO Secretary General Jens Stoltenberg said the alliance was “extremely focused on stepping up support” for Ukraine.
US President Joe Biden later announced $US1 billion ($A1.4 billion) worth of new weapons aid for Ukraine that sources familiar with the package said included anti-ship rocket systems, artillery rockets and rounds for howitzers.
Biden, who spoke with Ukraine’s President Volodymyr Zelenskiy by phone on Wednesday, also announced an additional $US225 million in humanitarian aid to Ukraine.
The bombardment of Sievierodonetsk’s Azot ammonia factory echoes the earlier siege of the Azovstal steelworks in the southern port of Mariupol, where hundreds of fighters and civilians took shelter from Russian shelling.
Those inside surrendered in mid-May and were taken into Russian custody.
Those inside Azot are surviving on water from wells and supplies of food brought in, the mayor said.
UK intelligence said the fighters could survive underground and Russian forces would likely remain focused on them, keeping them from attacking elsewhere.
But Ukrainian forces on the eastern front are exhausted and outnumbered, UK Defence Minister Ben Wallace said.
On Wednesday Zelenskiy urged more European sanctions against Russia.
He also said Russia’s territorial ambitions stretched beyond Ukraine to a swathe of eastern Europe from Poland to Bulgaria, without providing evidence for his claim.
In the Donbas, the sound of shelling could be heard near the town of Niu-York, where Ukrainian forces said Russia was throwing everything into the battle.
“For three and a half months we have been standing against the biggest country in the world,” a 22-year-old Ukrainian serviceman nicknamed “Viking” said.
“They have taken heavy casualties in vehicles and personnel but they don’t retreat.”
