Three Ukrainian soldiers have been killed in attacks by Russian-backed separatists in the past 24 hours, Kiev's military said on Wednesday, in fresh violation of a ceasefire regularly flouted since it was announced in September.

The deaths, which came as both Ukraine and Russia celebrated Eastern Orthodox Christmas, also coincided with fresh diplomatic efforts to organise a summit in Kazakhstan next week in an attempt to restore peace in eastern Ukraine.

Though large-scale clashes have diminished in a conflict in which more than 4,700 people have been killed, sporadic fighting has continued amid subdued New Year festivities and the run-up to Orthodox Christmas, which was observed quietly across Ukraine on Wednesday.

One soldier was shot dead by a sniper, while two others died in mortar and small arms attacks near the international airport in the industrial city of Donetsk, military spokesman Andriy Lysenko told journalists.

"In the past 24 hours, the situation in the east has not really changed. The terrorists carried out provocative attacks on the forces of the anti-terrorist operation in violation of the ceasefire," Lysenko said.

There was no confirmation from the separatist side of fresh clashes with government forces.

On the diplomatic front, Ukrainian President Petro Poroshenko is scheduled to meet Russia's Vladimir Putin and the leaders of France and Germany on Jan. 15 in the Kazakh capital Astana to hold further talks aimed at securing a lasting peace.

Ukraine and its Western allies want Russia to end its support for the separatists, who have declared pro-Russian 'people's republics' in eastern Ukraine, and to withdraw troops and military equipment from the region. Russia denies its forces have been involved in the conflict.

Ukraine and France say the meeting in Kazakhstan will take place only if there is a likelihood of real progress being achieved.