Russian forces have established full control over the Ukrainian city of Sievierodonetsk and the nearby town of Borivske, a senior defense ministry official said in a statement on Saturday.

Ukrainian officials said earlier in the day that their troops had withdrawn from Sievierodonetsk after a prolonged battle with regular Russian troops and fighters from the self-proclaimed Luhansk People's Republic (LPR).

"As a result of successful offensive operations, units of the people's militia of the LPR, with the support of Russian troops ... completely liberated the cities of Severodonetsk and Borivske," said defense ministry spokesman Igor Konashenkov.

He said the attack had thwarted what he called an Ukrainian attempt to turn the city's Azot chemical plant into a stubborn center of resistance.

Konashenkov said LPR fighters now controlled the plant, where several hundred citizens had been sheltering. He made no mention of their fate.