One battle could decide the fate of Ukraine's east. Its governor says it could be won in days if the West gave stronger weapons.

• Ukraine has been losing ground in the city of Severodonetsk.
• Zelenskyy said the fighting there has been tough, and the outcome could decide the fate of the Donbas region.

Ukrainian fighters in the eastern city of Severodonetsk could clear it of Russian forces within days if Western countries gave them long-range weapons, the region's governor said on Thursday.

Russia has made significant progress in Severodonetsk in recent days, and Ukrainian President Volodymyr Zelenskyy has described the fighting there as among the toughest of Russia's invasion so far.

On Thursday, Zelenskyy said that what happens there could decide the fate of the whole Donbas region— part of eastern Ukraine, where Russia has put its focus over the last few weeks and has for years been occupied by pro-Kremlin separatist forces.

Serhiy Haidai, the governor of the Luhansk region where Severodonetsk is located, said Western countries have the power to change the outcome of the battle there.

"If we get Western long-range weapons quickly, an artillery duel will begin, the Soviets will lose to the West, and our defenders can clean up Severodonetsk in two or three days," he said on Telegram on Thursday.

He also said Russia was using heavy artillery fire, and that civilians could not be evacuated.

Haidai said in an earlier update that Ukraine's forces had been pushed from the center of the city, and that Ukrainian troops only controlled the outskirts of the city, the BBC reported.

He told local media that Ukraine's troops were "defending" Severodonetsk and that it was "impossible to say the Russians completely control the city," the BBC reported.

Severodonetsk's mayor, Oleksandr Stryuk, said on Thursday morning that the situation in the city was "difficult but manageable," The Guardian reported.

He said Ukraine was holding its defensive lines, but that it was no longer possible to evacuate civilians from the city.

Russia has focused its efforts on Ukraine's east over the last few weeks, after its efforts to invade more of the country were hampered by logistical issues and unexpected resistance from Ukraine.

The Donbas is made up of Ukraine's Luhansk and Donetsk regions. Russia has long backed separatist areas there.

Western nations have been giving Ukraine weapons since Russia's invasion started, and while Ukrainian officials say they are grateful, they have called for more weapons, including heavier ones.

The UK announced this week that it was sending long-range missiles to Ukraine, and the US said last week that it would send some to Ukraine.