Ban said he was particularly concerned by the plight of civilians trapped in Debaltseve, a strategic railway hub linking two rebel-held cities.
"The rebel offensive continues and people are dying on a daily basis," he said in a statement released by his spokesman.
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He voiced support for a proposal by European OSCE monitors for a temporary truce in Debaltseve, which has been the focus of the fiercest fighting in a week.
Thousands of civilians have fled the beleaguered town over recent days and those remaining behind are trapped in basements without water or electricity.
Ban called on the separatist rebels and Ukrainian forces to "immediately move their military positions away from densely populated civilian areas."
The war in east Ukraine has claimed over 5,300 lives and driven over one million people from their homes in Europe`s worst humanitarian crisis since the Balkan war of the 1990s.
UN Chief Calls for Truce in Ukraine Frontline Town
05 February 2015
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UN Secretary-General Ban Ki-moon on Wednesday joined calls for a temporary truce to allow civilians to be evacuated from the frontline town of Debaltseve in east Ukraine.
