Russian troops entered the outskirts of the Ukrainian city of Sievierodonetsk, a regional governor said Monday, describing the fighting as "very fierce" in a city that become a key objective for Moscow's offensive in the Donbas.

Shelling killed two civilians and wounded five others as Russian troops advanced into the city's southeastern and northeastern areas fringes, Luhansk region Gov. Serhiy Gaidai said.

Incessant shelling has left Ukrainian forces defending ruins in Sievierodonetsk, but their refusal to withdraw has slowed a massive Russian offensive across the Donbas region in eastern Ukraine.