Russian President Vladimir Putin has ordered his defence minister to impose a 36-hour ceasefire on the Ukrainian frontline, beginning on Friday.
The ceasefire, scheduled to start at 12:00 Moscow time (09:00 GMT), will coincide with the Russian Orthodox Christmas.
Mr Putin asked Ukraine to reciprocate, but Kyiv quickly rejected the request. Ukrainian presidential adviser Mykhailo Podolyak said: "Keep hypocrisy to yourself."
Mr Putin's order followed an appeal from Patriarch Kirill, the head of the Russian Orthodox Church, on Thursday morning.
Kirill asked "all the parties involved" in the conflict to "cease fire and establish a Christmas truce".
The Russian Orthodox Church celebrates Christmas Day on 7 January, according to the Julian calendar. Mr Putin cited the patriarch's appeal as motivation for the ceasefire order.
The Russian Orthodox Church is by far the largest of the Eastern Orthodox churches, but there are others.