An "indefinite" cease-fire recently negotiated beween Ukraine's government and Russia-backed separatists in the east is due to start at midnight on December 24.
Ukrainian President Petro Poroshenko said the agreement reached on December 21 was a sign that his war-weary nation is on a road to lasting peace after nine previously negotiated cease-fires came unraveled.
"I expect that thanks to these measures, which come on the eve of the New Year and Christmas holidays, this cease-fire in eastern Ukraine will be a lasting one," he said.
Orthodox Christmas is observed on January 7.
Self-described leaders of the separatists also said the truce was a sign of hope after a recent upsurge in violence in the Donbas region.
United Nations Secretary-General Ban Ki-moon and German Foreign Minister Frank-Walter Steinmeier said they welcomed what Steinmeier called a "unanimous recommitment" to peace ahead of the holidays.
The two sides agreed to a similar holiday truce last year. It lasted for several weeks before fighting slowly resumed.
The last truce between the two sides was agreed in September and largely held until this month.