Germany and France demanded Friday that a crumbling Ukraine truce be "fully respected" even as pro-Russian rebels celebrated a battlefield victory in a strategic town and exchanged artillery fire elsewhere with government troops.
"The ceasefire has been violated several times," French President Francois Hollande said in a joint Paris media conference with German Chancellor Angela Merkel.
"It must now be fully respected along the entire frontline."
Merkel added that "we don't have any illusions" about how difficult it would be to get the ceasefire to take hold, but was "even more convinced" that the only solution was a truce that led to a negotiated peace.
French officials said the foreign ministers of Ukraine, Russia, Germany and France would meet in Paris next Tuesday to discuss the conflict.
The EU, US and Ukraine accuse Russia of being behind the hostilities. Moscow denies directly supporting the rebels.
While Merkel and Hollande met, pro-Russian rebels were taking victorious photos of each other in the east Ukrainian town of Debaltseve, a strategic transport hub they overran this week despite the ceasefire coming into force last Sunday.
The town was a graveyard of burnt-out Ukrainian army vehicles, craters and shattered buildings.
The battle for the town had involved non-stop shelling before the rebels stormed it for street-to-street fighting.
In an underground shelter littered with the detritus of days of survival, some 20 haggard women reproached the West for not doing enough to halt the violence. "You didn't defend us," one said.
- UN 'deeply worried' -
Friday also marked a year since the culmination of days of bloody protests in Kiev's Independence Square that led to the toppling of Russian-backed president Viktor Yanukovych.
Yanukovych's departure triggered a series of tumultuous events, including Russia's annexation of Crimea and, eventually, war in eastern Ukraine.
Ukrainian President Petro Poroshenko told a Kiev crowd marking the anniversary that "the revolution was a first, and most importantly, victorious battle in the war for our independence".
However, efforts by Ukraine's Western-backed government to stop the pro-Russian separatists have so far failed and it has come under criticism for losing key territory.
Around 2,500 Ukrainian soldiers who had been holding Debaltseve were forced to flee Wednesday after the rebels poured into it, in what Ukraine, the EU and US called a "clear violation" of the ceasefire.
Kiev said 13 troops were killed in the withdrawal and 110 seized by the separatists, with another 31 missing.
But the rebels said they found the bodies of 57 soldiers, as well as many abandoned weapons, including 28 tanks. They claimed to have taken hundreds of prisoners.
One rebel official in charge of human rights, Daria Morozova, said an initial exchange of prisoners with the Ukrainian side would take place on Saturday, the Interfax news agency reported.
There was no immediate reaction from Kiev, but a swap was agreed as part of the truce forged by Germany and France through all-night marathon negotiations last week in the Belarus capital Minsk.
Ukraine's military did, however, corroborate previous statements from rebel leaders that they have agreed a timeframe to start the simultaneous pull-back of heavy weapons from the front, a second step in the peace plan that was meant to follow the start of the truce.
The peace process aims to end a conflict that the UN estimates has killed nearly 5,700 people in the past 10 months.
Ukrainian officials said Friday two more soldiers had died, while rebels said army shelling killed a civilian in the rebel stronghold of Donetsk late Thursday.
Continuing fighting was reported around Donetsk and the government-held port city of Mariupol.
A Ukrainian military spokesman, Andriy Lysenko, said Russia had deployed "more than 20 tanks and 10 self-propelled guns" towards Novoazovsk, near Mariupol.
- 'Critical moment' -
Poroshenko has called for international peacekeepers to be deployed to keep the separatists and Russian forces in check.
However, in a phone call Thursday with Merkel, Hollande and Russian President Vladimir Putin, that appeal was ignored and the leaders agreed that the ceasefire should be applied regardless.
But EU president Donald Tusk said he was consulting EU leaders on how to increase "the costs of aggression" in eastern Ukraine.
Tusk did not specify what "costs" could be exacted, but his language echoed that preceding previous rounds of EU sanctions targeting Russia and Ukrainian rebel figures.