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.
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.
‘Not an indicator’;
Under the Minsk ceasefire agreed last week, the withdrawal of heavy weapons from front line areas was due to start no later than the second day after the truce came into effect and be completed within two weeks.
The withdrawal would create buffer zones 50-140km (30-85 miles) wide.
But a Ukrainian military spokesman quoted by Reuters news agency said there would be no withdrawal of heavy weapons yet because the rebels were violating the ceasefire. “The pre-condition for withdrawal of heavy weapons is fulfilling Point One of the Minsk agreements – the ceasefire. One hundred and twelve attacks are not an indicator of a ceasefire,” said Andriy Lysenko.
Rebel commanders also said there were no grounds yet to withdraw heavy weapons from the combat zone.
Rebel “defence minister” Vladimir Kononov said: “We will withdraw heavy weapons from the contact line if we get a definite sign that the Ukrainian side has started doing the same thing.” Observers from the Organisation for Security and Co-operation in Europe (OSCE) have been seeking to reach Debaltseve after being denied access by the rebels on Sunday.
German Chancellor Angela Merkel and French President Francois Hollande have called for the OSCE to be granted free access to eastern Ukraine.
Meanwhile, US state department spokeswoman Jen Psaki said the US was “gravely concerned by the deteriorating situation in and around Debaltseve” and called on “Russia and the separatists it backs to halt all attacks immediately”.
Elsewhere on the front line reports say the ceasefire has broadly been observed.
Under the agreement reached in Minsk last week, the ceasefire is only the first step.
Analysts point out that previous ceasefires initially appeared to be holding but eventually failed, and say the next 48 hours are critical.
Officials say more than 5,400 people have been killed since the conflict erupted in eastern Ukraine in April, but the UN believes the actual death toll to be much higher. (BBC)