A ceasefire that went into effect in eastern Ukraine appeared largely to be holding, officials said, except for around the strategic railway hub of Debaltseve.
Heavy fog muffled the sound of artillery, but regular shelling could still be heard from Luhanske, a town about nine miles to the north-west. Journalists were blocked from moving closer by Ukrainian troops, who said it was not safe to travel ahead.
The ceasefire has kindled slender hopes of reprieve from the conflict between government troops and Russian-backed separatists that has claimed more than 5,300 lives since it began in April.
Attention will be focused in the coming days on Debaltseve, where Ukrainian forces have for weeks been fending off severe onslaughts from the rebels. The town is a railway link between the main separatist-held cities of Donetsk and Luhansk.
This latest cessation of hostilities was agreed after a marathon session of diplomacy last week that brought together the leaders of Ukraine, Russia, Germany and France for talks in the capital of Belarus, Minsk.
Under the deal hammered out at those negotiations, the progress of the ceasefire is to be monitored by observers from the Organisation for Security and Cooperation in Europe.
The head of the OSCE monitoring mission, Ertugrul Apakan, said that the organisation has dispatched 20 patrols to monitor the state of the ceasefire.
"We made an attempt to send our monitors to Debaltseve, however our patrol has been refused access by the so-called DPR (the Donetsk People's Republic separatist movement)," Mr Apakan said.
Apakan said the cease-fire was being respected on the whole barring some isolated instances.
A spokesman for the Ukrainian army general staff, Vladislav Seleznyov, said during a morning briefing shelling was noted 10 times, with all but one incident occurring in the Debaltseve area. Another military spokesman, Andriy Lysenko, said nine Ukrainian troops had died over the previous day's unrest.
The rebels have in turn accused the Ukrainians of deploying artillery in the Debaltseve area shortly after midnight. Also, they argue that since they have fully encircled Debaltseve, the territory should be deemed as being theirs.
But Ukrainian President Petro Poroshenko, as he issued the ceasefire order at one minute after midnight Kiev time, said the road to the town remained open and that Ukrainian troops there had been resupplied with ammunition.
At an army checkpoint along the road to Debaltseve, a commander said the shelling appeared to have come from an area beyond Debaltseve controlled by "gangs other than the Russians and the separatists, such as Cossacks."
Donetsk, the separatist stronghold, was quiet todaywith no shelling from government forces, the Donetsk News Agency reported.
The hours before the ceasefire were marked by ferocious battles around Debaltseve, as Ukrainian armed forces undertook desperate attempts to gain control over a road linking the town to their rearguard.
The US State Department said satellite images from eastern Ukraine offer "credible pieces of evidence" that the Russian military has deployed larger amounts of artillery and multiple rocket launchers around Debaltseve to shell Ukrainian forces.
Russia has repeatedly denied Western claims that it has sent troops and equipment to aid the rebels.
Cessation of hostilities is only the first in a series of planned steps agreed to in Minsk.
Withdrawals of heavy weaponry from the front line, creating a zone roughly 30-85 miles wide, depending on the calibre of the weapons, are to begin tomorrow and be completed in two weeks. No provisions are envisioned for the withdrawal of troops.
The peace plan also requires the Ukrainian government to resume paying pensions and state benefits to citizens in rebel-held territory. Ukraine's financial blockade against the rebels has led to a catastrophic collapse in living standards in eastern Ukraine, depriving the poorest of any immediate means of support.