The ceasefire was broadly observed along the frontlines, but one commander said it did not apply to Debaltseve.
An extraordinary letter, addressed to major European bodies, compares the Ukraine crisis to WW2.
Russia reinforced rebels with 110 armored vehicles during marathon peace talks in Minsk, a spokesman said.
Leaders of Ukraine, Russia, Germany and France agree a deal to end fighting in Ukraine.
As peace talks begin in Belarus, the war continued to rage in Ukraine.
"We are united when it comes to support to Ukraine," the E.U.'s foreign policy chief, Federica Mogherini, says.
Pressure is building in Congress to supply weapons to Kiev's beleaguered forces.
The new ruling also allows commanders to fire at servicemen who are drunk while on duty.
The protest was generally peaceful, though the group remains at odds with the National Guard.
Both sides prepared to mobilize more forces for combat.
Violence in Ukraine's eastern Donbass regions is at its worst since the September ceasefire agreement
The separatist leader in Donetsk ruled out a ceasefire fighting intensified.
Since plans for another round of peace talks last week were abandoned, fighting has flared up again in Ukraine.
From a Russian cell, Ukrainian paratrooper and pilot Nadiya Savchenko protests with a hunger strike.
As fighting around Donetsk's airport intensified, a passenger bus came under heavy fire in eastern Ukraine Tuesday, killing at least 11 people.
Last week, Amnesty International warned that the country was heading for a "humanitarian catastrophe".
The move was made to help to end the pro-Russian uprising in the east of the country
There are 300 members of Chechnya's "Death" batallion, mostly former state security troops