A satellite image shows damaged Pavlograd Bridge in western Severodonetsk, Ukraine. Reuters

Regional governor Sergei Gaidai said on social media that some 70% of Sievierodonetsk was under enemy control, as the Russian offensive in the eastern Donbas region moved closer securing a breakthrough victory.

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Gaidai described the situation of Ukrainian soldiers holding out in the city as "difficult, but under control". But he said the destruction of the last bridge across the river to the twin city of Lysychansk meant any civilians still in Sievierodonetsk were trapped, and it was impossible to deliver humanitarian supplies.

Russian artillery also pounded the Azot chemical plant, where, according to Gaidai, hundreds of civilians were sheltering.

Smoke rises after shelling in Donetsk, Ukraine, on Monday. AFP

Ukraine has issued increasingly urgent calls for more Western heavy weapons to help defend Sievierodonetsk, which Kyiv says could hold the key to the battle for the eastern Donbas region and the course of the war, now in its fourth month.

Late on Monday, President Volodymyr Zelensky said the battle for the eastern Donbas would go down as one of the most brutal in European history. The region, comprising the provinces of Luhansk and Donetsk, is claimed by Russian separatists.

"For us, the price of this battle is very high. It is just scary," he said.

"We draw the attention of our partners daily to the fact that only a sufficient number of modern artillery for Ukraine will ensure our advantage."

A Russian soldier walks in front of the damaged Metallurgical Combine Azovstal plant in Mariupol. AP

Russia's main goal is to protect Donetsk and Luhansk, Kremlin spokesperson Dmitry Peskov said on Monday, after the leader of one of the separatist regions asked for additional forces from Moscow.

Ukraine needs 1,000 howitzers, 500 tanks and 1,000 drones among other heavy weapons, Presidential Adviser Mykhailo Podolyak said on Monday.

Moscow issued the latest of several recent reports saying it had destroyed US and European arms and equipment.

Russia's defence ministry said high-precision air-based missiles had struck near the railway station in Udachne northwest of Donetsk, hitting equipment that had been delivered to Ukrainian forces.

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

Ukraine's interior ministry on Telegram said that Udachne had been hit by a Russian strike overnight Sunday into Monday, without mentioning whether weapons had been targeted.

Moscow has criticised the United States and other nations for sending Ukraine weapons and has threatened to strike new targets if the West supplied long-range missiles.

The European Commission will recommend granting Ukraine official status as an EU candidate country, Politico reported late on Monday, citing several unnamed officials.

Commission President Ursula von der Leyen said on Saturday that the EU executive's opinion on Ukraine's request to join would be ready by the end of this week.

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