Volodymyr Zelenskyy has urged his compatriots to 'hold on' in the Donbas region, saying what happens there will determine the war against Moscow.

       "It is vital to stay in Donbas," said the Ukrainian president in a Tuesday evening address on Telegram. "The defence of the region is essential to give an indication of who will dominate in the coming weeks.”

       Zelenskyy made the remarks amid intense fighting in the eastern Donbas region.

       Russian and Ukrainian forces are currently engaged in a bloody battle over the two cities of Sievierodonetsk and Lysychansk, which were once home to 100,000 people each.

       “You have to hold on,” said the Ukrainian leader. “The more the enemy suffers losses there, the less strength he will have to continue his aggression.”

       Russia called on Ukraine to end its "absurd resistance" in Sievierodonetsk on Tuesday, and proposed a plan to evacuate civilians from the besieged city.

       The Russian Ministry of Defence said it would establish a "humanitarian corridor" for 12 hours on Wednesday in order to allow "the safe evacuation of all civilians, without exception."

       Past attempts to evacuate civilians elsewhere in Ukraine have routinely collapsed, with both sides blaming one another for their failure.

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       According to the Norwegian Refugee Council, some 500 civilians are trapped in the Azot factory in Sievierodonetsk.

       In a situation reminiscent of the Mariupol steel plant, where Ukrainian fighters and civilians held out against a Russian siege for weeks in desperate conditions, the NGO described them as being "almost completely cut off from all supplies."

       About 12,000 people remain in Sievierodonetsk, said Serhiy Haidai, governor of the eastern Luhansk region, Tuesday, adding that a mass evacuation was now "simply not possible".

       Taking Sievierodonetsk and Lysychansk is a critical objective of Moscow.

       It will allow Russian forces to press on towards the pivotal city of Sloviansk, which is key to capturing all of eastern Ukraine due to its west-central location in the Donbas.

       Russian troops currently control about 80 per cent of Sievierodonetsk.

       They have destroyed all three bridges leading out of the fiercely contested eastern city, according to Haidai.