Fighting raged in eastern Ukraine on 19 February, a day after pro-Russian separatists spurned a truce and forced out government troops to take over the strategic railway hub of Debaltseve.
Shelling continued in the region as also in another town further south, raising concerns in Kiev of a takeover bid for the major port of Mariupol.
One of the worst defeats suffered by Kiev in the 10-month-long conflict saw weary and demoralised soldiers withdraw from Debaltseve.
European and US officials were hoping the ceasefire would hold after the rebels' takeover of Debaltseve.
However, media reports say that shelling continued in the region as also in the rebel stronghold Donetsk.
An assault on Mariupol, a port town of 500,000 people and the biggest government-held city in the two rebellious eastern provinces, now worries Kiev.
The assault on 17 February killed 13 servicemen killed and wounded 157 during the withdrawal and a further 82 were still missing; 93 were taken prisoners.
"There are no words to describe it. Along the entire way we were blanketed with shots, wherever there were trees they fired at us from machine guns and grenade launchers. They used everything," Vadim, a soldier from Ukraine's 30th brigade, told Reuters in Artemivsk.
Relentless shelling was reported from the start of the ceasefire on 15 February until the withdrawal of troops, with the rebels maintaining that the ceasefire did not apply to Debaltseve.
The rebels had announced that they were pulling back heavy guns as required under the truce.
The leaders of Germany, France, Ukraine and Russia agreed on a fresh bid to enforce the ceasefire and ensure other terms of the peace deal were implemented.
Moscow has dismissed a call by Ukraine for United Nations peacekeepers to come to east Ukraine, insisting the Minsk agreements should be the basis for peace.
Western countries have accused Russia of equipping the rebels with advanced weaponry but Moscow denies this.
In a war of words, British Defence Secretary Michael Fallon said Putin posed a "real and present danger" to Estonia, Latvia and Lithuania and Nato was getting ready to repel any aggression. Moscow called the comments as beyond "diplomatic ethics".