Russia has previously denied claims it has tried to storm the steel works
Defence ministry spokesman Oleksandr Motuzyanyk gave few details and it was not clear whether Russian forces had launched a new operation at Azovstal.
Reuters could not verify the situation at the plant.
“The enemy continues to blockade our units in the area of the Azovstal factory, and is conducting storming operations with the support of tank and artillery fire,” he told an online briefing.
Raising the prospect of Russia stepping up its assault on the steel works further, hy het gesê: “The possibility of a renewal of its bombardment from Tu-22 M3 bombers is not excluded.”
Russia has previously denied assertions by Ukrainian officials that it has tried to storm the steel works.
Russian President Vladimir Putin said on April 21 that it was not necessary to storm the steel works but called for Russian forces to blockade the area “so not even a fly can get through”.
Ukrainian officials said days later that Russia had started an assault on Azovstal.
Ukraine has said all women, children and elderly civilians that were also in Azovstal have now left. Russia has said the evacuation of civilians from the plant is complete.
The bombed-out Azovstal steelworks became the last stronghold of Ukrainian defence forces in the region. 'N Geskatte 300 civilians were thought to be sheltering there to make a final stand to prevent a complete takeover of the city.
Op Sondag, Ukrainian fighters manning the plant vowed to continue their stand as long as they are alive.
“We will continue to fight as long as we are alive to repel the Russian occupiers,” Captain Sviatoslav Palamar, a deputy commander of Ukraine’s Azov Regiment, gesê.
“We don’t have much time, we are coming under intense shelling," hy het gesê, pleading with the international community to help to evacuate wounded soldiers from the plant.
Illia Samoilenko, an Azov fighter, said they still had weapons, munitions and water, and were prepared to fight as long as they must.
“We can die at any moment… Our message is don’t waste our efforts,” Mr Samoilenko added.