President Vladimir Putin has pledged to “intensify” attacks against Ukraine, following days of aerial bombardment by both sides in the long-running war.
Speaking during a visit to a military hospital in Moscow, Mr Putin said the military would continue targeting Ukrainian “military installations”.
He called an air raid on the Russian city of Belgorod by Ukraine a “deliberate strike against civilians”.
Twenty-five people were killed in Saturday’s attack, local officials say.
Speaking to Russian servicemen on Monday, Mr Putin said the war was turning in Moscow’s favour and he wanted the war to end quickly, but only on Russia’s terms.
He added that Ukraine’s Western supporters were the biggest obstacle to ending the conflict, but said their rhetoric was beginning to change as they started to realise they could not “destroy” Russia.
Ukrainian President Volodymyr Zelensky countered these claims in an interview with The Economist, saying Mr Putin’s suggestion that Russia was winning the war was only a “feeling”.
He highlighted Russia’s casualty figures in Ukraine, and said the opposing forces had been unable to take a single large city in 2023.
Mr Zelensky also expressed frustration with Kyiv’s Western allies, saying they had lost a sense of urgency.
The two leaders earlier delivered new year messages.
On Sunday, Mr Putin hailed Russian soldiers as “heroes” without explicitly referring to the war in Ukraine.
In his own address to mark the start of 2024, Mr Zelensky promised a sharp increase in the number of weapons produced by the country – pledging to build at least a million drones.
Russia and Ukraine have exchanged deadly attacks over the past few days.
Ukraine shelled the Russia-held Ukrainian cities of Donetsk on New Year’s Eve, according Moscow-installed officials, which killed at least four people and wounded 13.
And on Saturday, Ukrainian forces launched a series of strikes on targets in south-west Russia, including the strike on Belgorod which Mr Putin termed a “terrorist attack”.
Belgorod governor Vyacheslav Gladkov said on Monday that the death toll had risen to 25 following the death of a young child who was seriously injured in the attack.
“Today, a 4-year-old girl died in a regional children’s hospital. She was in a highly serious condition with combined injuries to the chest and internal organs,” Mr Gladkov wrote on the Telegram messaging app.
The girl’s death brought the number of child victims of the attack to five, the governor said. He added that 109 people were wounded in the air raid, with 45 currently in hospital.
Last week, Russia launched a widespread attack across several cities all across Ukraine, killing at least 45 people. Those strikes were described by Kyiv as Russia’s biggest missile bombardment of the war so far.