The brutal battle for the eastern Ukrainian city of Severodonetsk will determine the fate of the Donbass region, Ukrainian President Volodymyr Zelenskyy said, as Ukrainian troops claimed on Thursday to have pushed forward in intense street fighting in the city but said their only hope to turn the tide was more artillery to offset Russia's massive firepower.

In the south, Ukraine's Defense Ministry said it had captured new ground in a counter-attack in Kherson province, aiming at the biggest swathe of territory Russia has seized since its invasion in February.

The battle amid the ruins of Severodonetsk, a small industrial city, has become one of the war's bloodiest, with Russia concentrating its invasion force there. Both sides claim to have inflicted massive casualties.

In his nightly video address to the nation, Zelenskyy said the fate of the Donbass region was being decided in Severodonetsk, "a very brutal battle, very tough, perhaps one of the most difficult throughout this war."

"Severodonetsk remains the epicenter of the encounter in Donbass ... Largely, that is where the fate of our Donbass is being decided now," he added.

Severodonetsk and its twin city Lysychansk on the opposite bank of the Severskyi Donets river are the last Ukrainian-held parts of Luhansk province, which Moscow aims to seize as one of its principal war objectives.

In a rare update from Severodonetsk, the commander of Ukraine's Svoboda National Guard Battalion, Petro Kusyk, said Ukrainians were drawing the Russians into street fighting to neutralize Russia's artillery advantage.

"Yesterday was successful for us – we launched a counteroffensive and in some areas we managed to push them back one or two blocks. In others, they pushed us back, but just by a building or two," he said in a televised interview.

"Yesterday the occupiers suffered serious losses – if every day were like yesterday, this would all be over soon."

But he said his forces were suffering from a "catastrophic" lack of counter-battery artillery to fire back at Russia's guns.

Getting such weapons would transform the battlefield, allowing the Ukrainians to fend off Russian artillery, he said.

"Even without these systems, we are holding on fine. There is an order to hold our positions and we are holding them. It is unbelievable what the surgeons are doing without the proper equipment to save soldiers' lives."

'Western arms may end fight in 2-3 days'

Western long-range artillery would enable Ukraine to beat back Russian forces and capture Severodonetsk within days, a regional Ukrainian official said Thursday.

"As soon as we have long-range artillery to be able to conduct duels with Russian artillery, our special forces can clean up the city in two to three days," Lugansk regional governor Serhiy Gaidai said in an interview distributed on his official social media channels.

Gaidai also said that Ukrainian forces in the city remained "highly motivated" and that "everyone is holding their positions."

"Russia is constantly shelling areas controlled by Ukrainians with artillery," he added.

The U.S. and Britian have announced they are providing Kyiv with long-range precision artillery batteries, defying warnings from Russian leader Vladimir Putin.

Meanwhile, Severodonetsk Mayor Oleksandr Stryuk said Thursday around 10,000 civilians were still trapped inside the city – around a 10th of its pre-war population.

To the west of Severodonetsk, Russia is pushing from the north and south, trying to trap Ukrainian forces in the Donbass region comprising Luhansk and neighboring Donetsk province, blasting Ukrainian-held towns in their path with artillery.

Kherson counter-offensive

In the south, Moscow is trying to impose its rule on a tract of occupied territory spanning Kherson and Zaporizhzhia provinces, where it has installed proxy authorities who say they are planning referendums to join Russia.

The Ukrainian Defense Ministry said Thursday its forces had won back some territory in a counter-offensive in Kherson.

It gave no details but said the Russian forces had "suffered losses in manpower and equipment," mining territory as they were pushed back and erected barricades.

Ukraine had reported a counter-offensive in Kherson last week, claiming to have seized ground on the south bank of the Inhulets river forming a boundary of the province. The situation could not be independently confirmed.

Thousands of people have been killed and millions have fled since Moscow launched its "special military operation" to disarm and "denazify" its neighbor on Feb. 24. Ukraine and its allies call the invasion an unprovoked war of aggression.

Ukraine is one of the world's biggest grain and food oil exporters, and international attention has focused in recent weeks on the threat of international famine caused by Russia's blockade of Ukraine's Black Sea ports.

"Millions of people may starve if the Russian blockade of the Black Sea continues," Zelenskyy said on Thursday in televised remarks.

Moscow blames the global food crisis on Western sanctions against Russia, which it says are restricting its own grain exports. It says it is willing to allow Ukrainian ports to reopen for exports if Ukraine removes mines and meets other conditions. Kyiv says such offers are empty promises.