Ukraine's government and separatist rebels have failed to begin withdrawing heavy weapons from the front line, despite a Monday deadline.
The two sides were given until not more than two days after the latest truce came into effect to start the pullout, according to the (BBC).
The government said it would not pull back until fighting ended in the beleaguered town of Debaltseve.
Separatists say the agreement does not apply there because the town is surrounded.
They have offered Ukrainian troops encircled there a safe corridor to leave.
France, Germany and the US expressed concern at the continued fighting.
The Ukrainian military command said pro-Russian rebels had attacked 112 times since early Sunday, mostly around Debaltseve.
A Ukrainian officer said there was also fighting near Mariupol, a port city.
The rebels accused Ukrainian forces of shelling Donetsk airport. Meanwhile, further EU sanctions against Russia have gone into effect.
The new sanctions list targets 19 officials - most of them in the pro-Russian separatist strongholds of Donetsk and Luhansk, but also two Russian deputy defence ministers and a Russian celebrity singer and MP, Iosif Kobzon.