Ukraine dismissed as a trick a unilateral order by Russia for a 36-hour ceasefire starting today and the leaders of the United States and Germany said they were sending armoured fighting vehicles in a boost for the Kyiv government.

The US weapons package, to be announced later today, is expected to include about 50 Bradley Fighting Vehicles as part of security assistance totalling about US$2.8 billion, US officials said.

"Right now, the war in Ukraine is at a critical point," US President Joe Biden told reporters. "We have to do everything we can to help the Ukrainians resist Russian aggression."

Germany would provide Marder Infantry Fighting Vehicles, according to a joint statement on Thursday from Biden and Chancellor Olaf Scholz.

Both countries agreed to train Ukrainian soldiers on how to use them, it said. Germany would also supply a Patriot air defence battery to Ukraine, which has scored some battlefield successes since Russian forces invaded last February but has asked allies for heavier weapons.

Truce proposal

Ukrainian President Volodymyr Zelenskiy rejected out of hand a Russian order for a truce over Russian Orthodox Christmas starting at noon on Friday and ending at midnight on Saturday. He said it was a trick to halt the progress of Ukraine's forces in the eastern Donbas region and bring in more of Moscow's forces.

"They now want to use Christmas as a cover, albeit briefly, to stop the advances of our boys in Donbas and bring equipment, ammunition and mobilised troops closer to our positions," Zelenskiy said in his Thursday night video address.

"What will that give them? Only yet another increase in their total losses."

Biden suggested Putin's ceasefire offer was a sign of desperation. "I think he's trying to find some oxygen," he told reporters at the White House.

Russia's ambassador in Washington, Anatoly Antonov, responded on Facebook saying: "Washington is set on fighting with us 'to the last Ukrainian'."

On the decision to send Bradleys, he urged Washington to consider the "possible consequences of such a dangerous course."

Russia's Orthodox Church observes Christmas on Jan 7. Ukraine's main Orthodox Church has been recognised as independent by the church hierarchy since 2019 and rejects any notion of allegiance to the Moscow patriarch. Many Ukrainian believers have shifted their calendar to celebrate Christmas on Dec 25 as in the West.

Zelenskiy, pointedly speaking in Russian and not Ukrainian, said that ending the war meant "ending your country's aggression ... And the war will end either when your soldiers leave or we throw them out."

Dmitry Polyansky, head of Russia's permanent mission to the United Nations, wrote on Twitter that Ukraine's reaction was "one more reminder with whom we are fighting in #Ukraine - ruthless nationalist criminals who ... have no respect for sacred things".

No peace

In a phone call with Zelenskiy on Thursday, Turkish President Tayyip Erdogan said his government was ready to take on mediation and moderation duties to secure a lasting peace between Russia and Ukraine.

Putin told Erdogan separately on Thursday that Russia was open to dialogue over Ukraine but that Kyiv would have to accept the loss of territories claimed by Russia, the Kremlin said.

United Nations chief Antonio Guterres, at an event in Lisbon, said he believed the warring sides were "far from a moment in which a serious peace negotiation is possible".

The war, described by Putin as a "special military operation" to protect his country's security, has displaced millions, killed thousands of civilians and left Ukrainian cities, towns and villages in ruins.

In an update on Thursday, the Ukrainian prosecutor general's office said that at least 452 children have been killed and 877 children injured in the conflict.

In the capital Kyiv and the eastern city of Kramatorsk, people trying to go about their daily lives during wartime rejected Putin's ceasefire call.

"Look, we had Catholic Christmas, the fighting continued," Valerii, 30, in Kramatorsk said, adding that his town had suffered three or four hits on New Year's Eve alone.

"The fighting never stops, not on holidays, not on weekends. So to trust him? No."

In Kyiv, Nataliia Shkolka, 52, said: "We were under such bombing for New Year's Eve. I think it’s just hypocrisy on Putin's part."

The heaviest fighting of the war continues in eastern Ukraine, with the worst of it near the eastern city of Bakhmut.

Ukraine says Russia has lost thousands of troops despite seizing scant ground in months of futile waves of assaults on Bakhmut.

Near the front, Reuters saw explosions from outgoing artillery and smoke filling the sky.

"We are holding up. The guys are trying to hold up the defence,” said Viktor, a 39-year-old Ukrainian soldier driving an armoured vehicle out of Soledar, a salt-mining town on Bakhmut's northeastern outskirts.

The United States is of the view that Putin's ally Yevgeny Prigozhin, the founder of a powerful mercenary group, wants to take control of salt and gypsum from mines near Bakhmut, a White House official said

- Reuters