A shaky truce in Ukraine was already at risk on its second day Monday with both the Kiev government and pro-Russian separatists accusing each other of attacks holding up an agreed pull-back of heavy weapons from the frontline.
"There is no question at the moment of us withdrawing heavy weapons" because of persistent rebel attacks, a Ukrainian military spokesman, Vladyslav Seleznyov, told AFP.
"The withdrawal of military hardware can only happen under certain conditions and one of them is a full ceasefire," Eduard Basurin, a spokesman for the defence ministry of the self-proclaimed Donetsk People's Republic was quoted as saying by the rebels' official news agency.
The main hotspot was Debaltseve, a key transport hub located between Donetsk and Lugansk, where fighting is unabated.
AFP journalists and an OSCE monitoring team near Debaltseve observed shelling in the area. They were unable to enter the town because of the hostilities between thousands of government troops inside, and the rebels who have mostly surrounded it.
A municipal official who fled the town, Natalia Karabuta, told AFP that around 5,000 civilians were still trapped inside, with little food and water.
After a lull on Sunday, "today (Monday) it all flared up again, and non-stop explosions were heard," she said.
The separatists also said Ukrainian troops had fired on Donetsk airport as journalists were being shown around. No casualties were reported.
Kiev said five Ukrainian troops have been killed and 25 wounded in the town of Shyrokin, near the coastal city of Mariupol, since the ceasefire started.
Under the terms of a European-mediated peace plan agreed last week, two days of a "comprehensive" ceasefire were meant to lead to a withdrawal of heavy weapons from the frontline, starting at midnight (2200 GMT) Monday.
Other steps, including a prisoner swap and negotiations over increased autonomy for separatist-ruled areas, were then to follow.
Ukraine's Foreign Minister Pavlo Klimkin said during a visit to Bulgaria that "the Ukraine armed forces are fully observing the ceasefire regime but unfortunately in response we have received 112... attacks in the past 24 hours from the terrorists of Donetsk and Lugansk".
- EU blacklists Russian officials -
While tensions rose on the ground, the European Union upped the ante on the diplomatic front, adding two Russian deputy defence ministers, Anatoly Antonov and Arkady Bakhin, to its travel-ban and asset-freeze blacklist for allegedly sending Russian troops and materiel in to support the Ukrainian insurgency.
Three other Russians, including two lawmakers, and 14 Ukrainians acting as rebel military or political officials in the self-declared republics of Donetsk and Lugansk, were also blacklisted, along with nine entities. The sanctions were agreed last month but put on hold while France and Germany worked to secure the ceasefire.
Russia denies repeated allegations it is sending troops and tanks to support the pro-Russian rebels. The West though has imposed sanctions that, along with the sharp decline in oil prices, are accelerating the Russian economy's slide into recession.
The internationally backed peace deal aims to end the bitter Ukraine conflict that has claimed more than 5,480 lives since it started in April last year, and has sent East-West relations to lows not seen since the Cold War.
Ukrainian President Petro Poroshenko has said he could order martial law across the country if diplomacy fails.
A previous truce agreed in September similarly dampened fighting initially before eventually falling apart under the weight of constant breaches.