Ukrainian President Petro Poroshenko has said government forces were completing a "planned and organized" withdrawal from the eastern town of Debaltseve, which has been at the epicenter of fighting between Ukrainian troops and pro-Russian separatists in recent weeks.

"As of now we can say that 80 percent of our units have left," Poroshenko said, adding that two more columns were expected to pull out.

Hostilities have continued despite a cease-fire brokered by European leaders last week and supposed to have taken effect on February 15.

Debaltseve is a key railway hub linking the rebel-held cities of Donetsk and Luhansk.

The European Union's foreign affairs head, Federica Mogherini, on February 18 condemned the rebel offensive against Debaltseve as a "clear violation" of the cease-fire.

Russian Foreign Minister Serigei Lavrov says the truce is in place in almost all frontline areas except Debaltseve.