Ukraine's separatist east passed the night into Tuesday without any shooting, President Petro Poroshenko said, hailing the first such stretch of calm as a positive signal for the next steps in a peace plan.
Army chief of staff Viktor Muzhenko also stressed progress had been made on the implementation of the cease-fire, but said one Ukrainian soldier had since been killed on Tuesday.
Ukraine is under pressure from Western backers to defuse the conflict, which has left many people struggling to survive the winter, while the cost of the fighting has pushed former Soviet republic towards the brink of bankruptcy.
A 12-point cease-fire protocol was worked out in September to end the conflict between government forces and Russian-backed separatists in which more than 4,700 people have been killed.
But the truce was repeatedly flouted and Kiev made clear it would not carry out ensuing steps stipulated by the accord until the guns fell silent.
"Today was the first night when we didn't have a single shelling," Poroshenko said at a partly-televised meeting with security aides. "Today we face the extremely crucial task of implementing the peace plan."
Rebels disagreed with Poroshenko's assessment, accusing Kiev of further artillery bursts overnight. But his comments sounded an upbeat note ahead of a two-day visit to Kiev by the new European Union foreign policy chief, Federica Mogherini.
That optimism was later tempered by the report of a soldier killed on Tuesday near the contested Donetsk Airport, the first Ukrainian loss in six days. But the Kiev military highlighted a decline in the intensity of attacks — to an average of 8-10 incidents of shelling per day from a previous 70-80.
Last week, prospects for a fresh round of peace talks between a "contact group" comprising Ukraine, Russia and the Organization for Security and Cooperation in Europe (OSCE) watchdog were dashed by renewed clashes in the east.
On Monday, senior Ukrainian presidential official Valeriy Chaliy said the contact group should meet "as soon as possible," but no date had been agreed.
Russia denies Ukrainian accusations of intervening militarily on the side of the eastern rebels. It has also called for a new round of peace talks on the conflict and on Monday urged Kiev to allow more autonomy to Russian-speaking eastern areas of Ukraine.
Contradicting Poroshenko's reports of a fully-observed truce overnight, the separatist self-proclaimed Donetsk People's Republic accused government troops of carrying out artillery strikes on rebel positions.