The UN on Friday said the humanitarian situation in eastern Ukraine is "extremely alarming" and continues to deteriorate, four months into the Russian invasion. 

"Nearly four months since the start of the war, the humanitarian situation across Ukraine -- particularly in the eastern Donbas -- is extremely alarming and continues to deteriorate rapidly," the UN's humanitarian agency, OCHA, said in a statement. 

It said the situation is "particularly worrying in and around Severodonetsk" -- the eastern Ukrainian city where bloody battles have raged for weeks. 

Hundreds of civilians are believed to be trapped in the city, with some sheltering in the local chemical plant.

The UN said there is "diminishing access to clean water, food, sanitation and electricity" in the city, the statement said.  

It said that as "active hostilities continued to escalate" in eastern Ukraine, the war is "taking an enormous toll on civilians, including aid workers".

"Despite enormous access challenges, the UN and humanitarian partners have reached over 8.8 million people across Ukraine since the war started," it added.