The Russian army has full control over Severodonetsk, its mayor said on Saturday after heavy fighting on the eastern front over the key city.

Severodonetsk falls within the Lugansk People's Republic (LPR), but mayor Oleksandr Striuk claimed that the city "has been fully occupied by the Russians."

Kiev's forces on Friday had been forced to retreat from Severodonetsk, a regional governor said, with the aim of setting up camp at the neighboring city of Lysychansk.

"Ukrainian armed forces will have to retreat from Severodonetsk. They have received an order to do so," Lugansk governor Sergiy Gaiday said on Telegram.

"Remaining in positions that have been relentlessly shelled for months just doesn't make sense," he explained. The city has been "nearly turned to rubble" by frequent bombardment.

Severodonetsk is home to the Azot chemical plant, where the Russian armed forces had hundreds of Ukrainian soldiers holed up for weeks in light of the confrontations in the area. The plant also had up to 500 civilians who had been hiding from shelling in its bomb shelter, and despite the site having more civilians than Ukrainian soldiers, they were concentrated in other parts of Azot.

Moscow had announced evacuating more than 800 civilians sheltering there after taking control of the factory.

If Russia were to push into Lysychansk and take control of the city, the Russian and pro-Russian forces would have full control of the LPR and allow them to take push further into the Donbass region.

Ukraine has said on Tuesday that the Russian armed forces made major advances in Donbass, taking control of Toshkiva, a village that lies between the two cities of Severdonetsk and Lysychansk on the frontline between Kiev's and Moscow's forces.

The cities of Severodonetsk and Lysychansk, separated by a river, are the final sections of Lugansk still under Ukrainian control. Now, only Lysychansk remains under Ukrainian control.

Before the war, Toshkiva had a population of around 5,000. It is approximately 25 km south of Severodonetsk, a city that has been seeing intense fighting between Kiev and Moscow's forces.

The battle for Severdonetsk has been shifting in the favor of the Russians for a while now, with Russia's National Defense Control Center chief Mikhail Mizintsev announcing in early June that the Ukrainian forces in the city had lost up to 90% of their military troops.