Smoke rises after a military strike on a compound of Sievierodonetsk's Azot Chemical Plant, amid Russia's attack on Ukraine, Lysychansk, Luhansk region, Ukraine June 10, 2022. Picture taken June 10, 2022.
Smoke rises after a military strike on a compound of Sievierodonetsk's Azot Chemical Plant, amid Russia's attack on Ukraine, Lysychansk, Luhansk region, Ukraine June 10, 2022. Picture taken June 10, 2022. Reuters / STRINGER

Ukraine ignored a Russian ultimatum to surrender the eastern city of Sievierodonetsk on Wednesday as Washington urged NATO defence ministers weighing more military support for Kyiv not to lose focus, saying the stakes were too high.

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.

"We are trying to push the enemy towards the city centre ... This is an ongoing situation with partial successes and tactical retreats," Stryuk said on television. He made no reference to the Russian ultimatum.

"The escape routes are dangerous, but there are some."

Moscow had said it would let civilians evacuate from 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 8 a.m. Moscow time (0500 GMT) deadline.

Reuters could not immediately verify the battlefield accounts.

Luhansk is one of two eastern provinces Moscow claims on behalf of separatist proxies. Together they make up the Donbas, an industrial Ukrainian region where Russia has focused its assault after failing to take Ukraine's capital Kyiv in March.

Addressing dozens of NATO defence ministers meeting in Brussels to debate their next moves, U.S. 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.

ECHOES OF MARIUPOL

The Azot bombardment 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.

The sprawling ammonia factory in Sievierodonetsk was founded under Soviet leader Josef Stalin. Those inside were surviving on water from wells and supplies of food brought in, the mayor said, but the situation was critical.

British 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, British Defence Minister Ben Wallace said.

Kyiv has said 100-200 of its soldiers are being killed every day, with hundreds more wounded in some of the bloodiest fighting since Russia's Feb. 24 invasion.

"We have to hold strong ... The more losses the enemy suffers, (the) less strength it will have to pursue its aggression," Zelenskiy said in an address late Tuesday. On Wednesday he called for more European sanctions against Russia.

'BRUSSELS, WE ARE WAITING'

Western countries have promised NATO-standard weapons - including advanced U.S. rockets. But deploying them is taking time and Zelenskiy said Ukraine does not have enough anti-missile systems and there was no justification for delays.

His adviser, Mykhailo Podolyak, said the defenders of Sievierodonetsk wanted to know when the weapons would arrive. "Brussels, we are waiting for a decision," he wrote on Twitter.

NATO Secretary General Jens Stoltenberg said the alliance was "extremely focused on stepping up support" for Ukraine. The gathering in Brussels is the third time the group of nearly 50 countries are meeting to coordinate help for Kyiv.

In May, the U.S. Senate passed a bill to provide $40 billion in additional aid to Ukraine and has promised longer-range rocket systems, drones and advanced artillery.

Russia gives no regular figures of its own losses but Western countries say they have been massive as President Vladimir Putin seeks full control of the Donbas and a swathe of southern Ukraine. Putin calls the war a special military operation against Ukrainian nationalists.

Elsewhere in the Donbas, Ukraine says Russia plans to attack Sloviansk from the north and along a front near Bakhmut to the south. The sound of shelling could be heard 40 km (25 miles) south of Bakhmut 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."

The conflict has sent grain prices soaring and Western sanctions against Russia have driven up oil prices. Ukraine's agriculture minister told Reuters the invasion would create a global wheat shortage for at least three seasons by keeping much of the Ukrainian crop from markets.

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