Smoke rises after a military strike on a compound of Sievierodonetsk's Azot Chemical Plant, Ukraine. Reuters

Ukraine is calling for an increase in Western heavy weapons after Russia committed the bulk of its firepower to the eastern Donbas region, a topic expected to feature prominently at a meeting of NATO defence ministers on Wednesday in Brussels.

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Zelensky pleads for arms as Russian forces lay siege to Severodonetsk

No way out for Ukrainians in embattled city

Ukraine says more than 500 civilians are trapped alongside soldiers inside the Azot chemical factory where its forces have resisted weeks of Russian bombardment and assaults that have reduced much of Sievierodonetsk to ruins.

Fighters should "stop their senseless resistance and lay down arms" from 8 a.m. Moscow time (0500 GMT)," Mikhail Mizintsev, head of Russia's National Defence Management Centre told the Interfax news agency.

A man holds his baby inside Azot chemical plant's bomb shelter in Sievierodonetsk, Luhansk, Ukraine. Reuters

Civilians would be let out through a humanitarian corridor, Mizintsev said.

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.

Shelling on Azot was so heavy that "people can no longer stand it in the shelters, their psychological state is on edge," said regional governor Serhiy Gaidai of Luhansk, one of two eastern provinces Moscow claims on behalf of separatist proxies.

Ukrainian servicemen ride an American 155 mm turreted self-propelled howitzer M109 in Donetsk. Reuters

The Russian assault on Luhansk's Sievierodonetsk — a city of barely more than 100,000 people before the war — is currently the focal point of what has been called the battle of the Donbas.

Kyiv has said 100-200 of its soldiers are killed each day, with hundreds more wounded.

'Unable to leave'

Russia gives no regular figures of its own losses but Western countries say they have been massive as President Vladimir Putin seeks to force Kyiv to cede full control of two provinces, Luhansk and Donetsk, collectively known as the Donbas.

Momentum in Sievierodonetsk has shifted several times over the past few weeks — with Russia concentrating its overwhelming artillery firepower on urban districts to obliterate resistance, then sending in ground troops vulnerable to counter-attacks.

A woman stands above Nadiia Chuhai lying in her bed inside a shelter in Sievierodonetsk, Ukraine. Reuters

Elsewhere in the Donbas, Ukraine says Russia plans to assault Sloviansk from the north and along a front near Bakhmut to the south.

In Donetsk province, critical infrastructure including homes, schools, hospitals and markets have been attacked over the past week, United Nations spokesman Stephane Dujarric told reporters in New York.

"This has made life nearly unbearable for people who are also facing severe water shortages, and at times are unable to leave their homes for days on end due to the fighting," Dujarric said.

To the south, Ukraine's military said it had conducted three air strikes against troop concentrations, fuel depots and military equipment in the Kherson region.

Reuters