An agreement is due to come into effect from Sunday under a peace accord that also envisages a withdrawal of the heavy weapons responsible for casualties, in the conflict that broke out almost a year ago.
A military spokesman, Anatoly Stelmakh, said in a television interview, that “there has been no lull, moreover rebels continue attacks on Debaltseve,” a strategic transport hub northeast of Donetsk city, that has been the focus of some of the fiercest fighting in recent weeks.
The Ukrainian military separately said the situation remained tense in parts of the contested Luhansk region.
The Ukraine President, Petro Poroshenko, also accused Russia of “significantly increasing” its offensive despite the peace agreement reached in Minsk on Thursday.
Shelling was heard in the rebel-held city of Donetsk early on Saturday.
Reports say as the time gets closer for the ceasefire, fears are rising that it won’t be observed.
More than a dozen civilians are said to have died in shelling in eastern Ukraine on Friday.
It is unclear who was behind the shelling but both the Ukrainian military and pro-Russian rebels in the eastern Donetsk and Luhansk regions accuse each other of the attack.
Speaking earlier, President Poroshenko said despite what had been agreed in Minsk, “Russia’s offensive operations have intensified”.
“We are still convinced that the Minsk achievements are in a big danger,” he added.
“Ahead of midnight, rebels are trying to complete tactically important plans to enlarge the territory under their control, primarily in the direction of Debaltseve,” spokesman Andriy Lysenko said