In the latest developments, the Ukrainian General Staff announced that the Russian forces expelled the Ukrainian army from the center of Severodonetsk, the strategic city in eastern Ukraine where fierce battles have been taking place for weeks. 

"The enemy, with artillery support, launched an attack on Severodonetsk, which achieved partial success and expelled our units from the city center," the army said in its morning briefing on Facebook, stressing that the battles were "continuing."

Sergey Gaidai, the Ukrainian governor of Lugansk, confirmed the exit of Ukrainian forces from the city center, which is the administrative center of the part of the region under the control of Kyiv. On Monday morning, he wrote on Facebook: "The battles continue in the streets. The Russians continue to destroy the city," posting pictures of destroyed or burning buildings. He pointed out that the Russian bombing targeted a chemical factory where civilians were hiding and targeted sewage stations in the city.

Ukrainian officials said that Russian forces blew up a bridge linking the street-stricken Ukrainian city of Severodonetsk to another city across the river, cutting off a possible evacuation route for civilians.

Ukrainian President Volodymyr Zelensky likened the situation in Severodonetsk to a grave, which has become the focus of the battle for control of the Donbas industrial region in the east, consisting of Luhansk and Donetsk.

The commander of the Ukrainian army said that the active fighting against Russia extends over 1,000 km, stressing that Russia is not advancing in Lugansk and is again bombing Kharkiv, Chernihiv and Sumy. He added that the security is investigating the suspicion of the presence of 50 collaborators with the Russian army.

For its part, Moscow confirmed on Sunday that it had "destroyed a large warehouse" in western Ukraine for weapons sent from Western countries, at a time when fierce battles are taking place in Severodonetsk in the east of the country, where it appears that Ukrainian forces are facing difficulties in confronting the Russians.

"The Kalibr missiles were launched from the sea, near Chortkev and destroyed a large warehouse of anti-tank missile systems, man-portable air defence systems and missiles supplied by the United States and European countries to the Kyiv system," the Russian Defense Ministry said in a statement.

The Russian army did not specify the timing of this strike, but the Ukrainian authorities in this small town in the country's West announced that on Saturday evening, it had wounded at least 22 people, including civilians, and damaged a military site.

Commenting on this, President Zelensky said in his evening video message on Sunday that "there was no tactical or strategic target for this strike, as is the case in the vast majority of other Russian strikes, describing the strike as" just terrorism."

In the east, the Ukrainian General Staff announced on Sunday morning that Russian forces were launching attacks on Severodonetsk "without achieving success," noting that Ukrainian soldiers repulsed the Moscow army near Vrobivka, Mykolaivka and Vasevka.

Control of Severodonetsk opens the way for Moscow to another significant city, Kramatorsk, in the Donbas Basin, a predominantly Russian-speaking region that Russia wants to control entirely. Pro-Russian separatists have controlled parts of this mining-rich region since 2014.

"The situation in Severodonetsk is tough," Lugansk region governor Sergey Gaidai said via Telegram. He added that the Russian forces wanted to "completely close the city" and prevent any passage of men and ammunition, pointing out that he feared the enemy would use "all its precautions to seize the city" within 48 hours.

In the south, in the Donetsk region, the Ukrainian presidency said that "the Russians (reinforce) their efforts to destroy basic infrastructure."

At the other end of the front line, in Mykolaiv, an important port on the estuary of the Dnieper River in the south, the Russian advance has stalled on the outskirts of the city, according to a field team of AFP correspondents.

The Ukrainian Operations Command stated that the Russian forces fired missiles at the outskirts of this city, which were "continuous fire aimed at psychologically putting pressure on the civilian population."