A local resident cooks outside her house in Debaltseve, February 4, 2015. [Photo/Agencies]

UNITED NATIONS - UN Secretary-General Ban Ki-moon on Wednesday said that he "remains gravely concerned over the situation in eastern Ukraine", and reiterated his call for "a sustainable ceasefire to take hold and for urgent diplomatic and political action".

"The secretary-general remains gravely concerned over the situation in eastern Ukraine, particularly the plight of civilians trapped without basic services in the city of Debaltseve," said a statement issued here by Ban's spokesman.

"The rebel offensive continues and civilians are dying on a daily basis," the statement said. "He condemns in the strongest terms reports of indiscriminate shelling and calls on both sides to immediately move their military positions away from densely populated civilian areas."

In eastern Ukraine, battles are raging between government forces and rebels for control of a strategic transport hub.

Intense artillery fire thundered around the town of Debaltseve on Sunday, which is a key position between the rebel bastions of Donetsk and Luhansk, where rebels are trying to encircle Ukrainian troops.

Ukrainian military spokesman Volodymyr Polyovyi in Kiev said "constant battles" were going on around Debaltseve, but pledged that government forces would not give up control of the last remaining road into the town.