Ukrainian President Petro Poroshenko ordered government forces to cease firing at midnight Sunday Ukrainian time, in line with a peace agreement reached in Belarus last Thursday.
Earlier, rebel leaders in eastern Ukraine also told their forces to observe the truce.
Part of Poroshenko’s meeting with defence chiefs was broadcast live on Ukrainian TV ahead of the midnight deadline.
“I will deliberately not say what Ukraine will do if a peace process collapses. I will say only that after being slapped in one cheek we will not show the other one. And let God forgive me, I hope very much that this very last chance to start a long and difficult peace process – aimed at finding a political solution in Donbas – will not be missed.”
Mistrust remains high on both sides after a similar peace deal last September failed to hold and fighting has intensified in recent days as both sides appeared to shore up their positions.