Ukrainian and Russian troops fought street by street for control of the industrial city of Sievierodonetsk on Monday in the pivotal battle of the Kremlin offensive in Ukraine’s eastern Donbas region.

Which side had the upper hand remained unclear. Russian forces had the numerical advantage and the situation was “difficult”, but Ukraine had “every chance” to fight back, its President Volodymyr Zelensky said after a regional official suggested Kyiv had lost ground.

Ukraine’s defence ministry said Russia was throwing troops and equipment into its drive to capture Sievierodonetsk, the largest remaining Ukrainian-held city in Luhansk province.

It has become the main target of the Russian offensive in the Donbas – made up of Luhansk and Donetsk provinces – as the Kremlin’s invasion grinds on in a war of attrition that has seen cities laid waste by artillery bombardments.

Ukrainian defenders had over the weekend pushed back the Russians as they seemed close to victory in Sievierodonetsk.

“Our defenders managed to undertake a counter-attack …But now the situation has worsened a little for us again,” Luhansk governor Serhiy Gaidai told state television.

Sievierodonetsk Mayor Oleksandr Stryuk said street fighting was raging and neither side was preparing to withdraw.

“The situation is difficult in the east,” President Zelensky told a media briefing in the capital Kyiv. “We are in control of the situation, there are more (Russians), they are more powerful, but we have every chance to fight.

“If there is a (Russian) breakthrough in Donbas, it will be very difficult,” he added.

Both sides say they have inflicted huge casualties on each other.

Smoke rises in the city of Severodonetsk

Russia says it is on a mission to “liberate” the Donbas – which has been partly held by separatist proxies of Moscow since 2014 – after Ukrainian forces pushed its troops back from the capital Kyiv and Ukraine’s second biggest city Kharkiv in the war’s early stages.

President Zelensky sought to rally his troops on Sunday with a visit to two cities close to the front lines.

“What you all deserve is victory – that is the most important thing. But not at any cost,” Zelensky said in a video.

He said he had travelled to Lysychansk, south of Sievierodonetsk, and Soledar – rare outings for him outside of Kyiv since the start of the Russian invasion.

Russia calls its action in Ukraine a “special military operation” mounted to stamp out what it sees as threats to its own security. Ukraine and its Western allies dismiss this as nonsense and say Russia’s is an unprovoked war to grab territory that risks turning into a wider European conflict.

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Putin warning

In a boost for Kyiv, Britain said it would supply Ukraine with multiple-launch rocket systems that can strike targets up to 80km away. The systems would give the Ukrainians the more precise, long-range firepower needed to reach Russian artillery batteries, a key component of Moscow’s battle plans.

The British move was coordinated with the United States, which last week pledged to supply Kyiv with advanced rocket systems.

Zelensky said Kyiv was gradually receiving “specific anti-ship systems” from certain countries, and that these would be the best way to end a Russian blockade of Ukrainian Black Seaports preventing grain exports.

A tank destroyed during Russian attacks at Zahaltsi village in Kyiv

Russian Foreign Minister Sergei Lavrov said Moscow would respond to Western deliveries of long-range weapons to Ukraine by pushing Ukrainian forces further back from Russia’s border.

On Sunday, President Vladimir Putin said Russia would strike new targets if the West supplied longer-range missiles to Ukraine. The same day, Russian missiles hit Kyiv for the first time in more than a month. Ukraine said the strike hit a railcar repair works, while Moscow said it had destroyed tanks sent by Eastern European countries to Ukraine.

A building destroyed by a strike in Lysytsansk

Destroy tanks

Ukraine’s defence ministry said Russian forces were also thrusting towards Sloviansk, which lies about 85km to the west of Sievierodonetsk.

Some 60km to the south, on the front line near Bakhmut, Ukrainian soldiers said the situation was difficult but they had no choice but to push back the Russians.

A unit commander who gave his name as Maxym appealed for more arms from Ukraine’s allies.

“With more anti-tank weapons we would be able to destroy their tanks, to cause maximal damage and the enemy will be forced to flee from where they came,” he told Reuters.

“…We will fight for every piece of this land.”

Russian forces were fortifying their positions in the Kharkiv region and shelling Ukrainian positions to keep hold of the territory they had occupied, Ukraine’s military general staff said.

It said Russia was targeting civilian infrastructure in several towns and the regional administration said three civilians were killed and 10 wounded in shelling.

It was not possible to verify the toll. Moscow denies targeting civilians.