Vladimir Putin’s promise of a 36-hour truce in his Ukraine war has been mocked by the sound of artillery and incoming missiles as fierce fighting continues.

Russian and Ukrainian forces have continues to exchange artillery fire  after Moscow said it had ordered its troops to stop shooting for a unilateral truce – a move firmly rejected by Kyiv.

President Vladimir Putin ordered the 36-hour ceasefire from midday on Friday to observe Russian Orthodox Christmas.

Ukraine has said it has no intention to stop fighting, rejecting the purported truce as a stunt by Moscow to buy time to reinforce troops that have taken heavy losses this week.

“What ceasefire? Can you hear?” said a Ukrainian soldier, using the nom de guerre Vyshnya, as an explosion rang out in the distance at the front line near Kreminna in eastern Ukraine.

Russia’s defence ministry said its troops began observing the ceasefire from noon Moscow time (0900 GMT) “along the entire line of contact” but said Ukraine had kept up shelling populated areas and military positions.

Claim and counterclaim

Reuters heard explosions of what Ukrainian troops at the front line described as incoming Russian rocket fire.

Ukrainians fired back from tanks.

The Ukrainian troops said it was quieter than many other days because snowy weather had made it hard to fly drones and spot targets.

It was not immediately possible to establish whether there was any reduction in the intensity of fighting at other locations.

One witness in the Russian-occupied regional capital Donetsk also described outgoing artillery fired from pro-Russian positions on the city’s outskirts after the truce was meant to take effect.

The Ukrainian governor of the front line eastern Luhansk province, Serhiy Haidai, said the Russians had shelled Ukrainian positions 14 times and stormed one settlement three times in the first three hours of the purported ceasefire.

Russia’s Orthodox Church observes Christmas on January 7.

The main Orthodox Church in Ukraine has rejected the authority of Moscow, and many Ukrainian believers shifted their calendar to celebrate Christmas on December 25, as in the West.

Putin attended a service by himself inside a Kremlin cathedral rather than joining other worshippers in a public celebration.

State television showed two live clips of Putin inside the gilded Cathedral of the Annunciation as Orthodox priests conducted the midnight service, known as the Divine Liturgy.

More billions on the way from US

Washington unveiled its latest $US3.75 billion ($A5.47 billion) package of military aid for Ukraine and allies affected by the war, for the first time sending the United States army’s workhorse Bradley Fighting Vehicles.

Germany and France also pledged armoured vehicles, finally fulfilling one of Kyiv’s most urgent requests from its allies for armour to defeat Russian tanks in mechanised battles.

Ukrainian President Volodymyr Zelenskiy, who pleaded for the Bradleys in Washington last month on his first trip abroad since the war began, said on Friday they were “exactly what is needed”.

Shortly before the ceasefire was meant to start, rockets slammed into a residential building in Kramatorsk, close to the eastern front line, damaging 14 homes, although with no casualties as many people have fled.

One rescue worker was killed and four others injured when Russian forces shelled a fire department in the southern Ukrainian city of Kherson before the deadline early on Friday, the regional governor said.

Reuters could not immediately verify this.

Zelenskiy has rejected the Russian ceasefire out of hand as a ploy for Russia to buy time to bring in equipment and ammunition after sustaining crippling losses at the front line.

Scores of Russian troops were killed in one attack over the New Year weekend.

-AAP