Ukraine's President Petro Poroshenko has formally given the order for a ceasefire in the eastern part of the country.
Poroshenko has demanded the country's armed forces to hold their fire as the ceasefire agreed in Minsk early on Thursday went into force.
Under the agreement, Ukrainian forces and the eastern separatist rebels were to begin pulling back their heavy weaponry this week to form a buffer zone.
Poroshenko said he guaranteed that Ukrainian forces would fulfill their side of the agreement.
"We strongly demand that all points of the Minsk protocol, the Minsk memorandum and Minsk agreement are immediately fulfilled. And we count on the unity of the whole world for their solidarity with Ukraine in our fight for peace. We guarantee that all Ukrainian armed forces will fulfil the order of the president of Ukraine."
The ceasefire began one minute after midnight local time or 2200 GMT.
There were no immediate indications of whether either side in the conflict was observing it.
At present, rival claims to Debaltseve, a strategic railway hub now controlled by the government, suggest conflict is not far behind.
The hours before the ceasefire were marked by ferocious battles as Ukrainian forces undertook desperate efforts to hold onto Debaltseve.
Separatists rebels have said they will not consider any battles for Debaltseve to be a violation of the ceasefire.
