By Kathryn Armstrong for the BBC
A Ukrainian medic treats a wounded serviceman in the Donetsk region on 30 November 2023. Photo: AFP/ Genya Savilov
Ukraine's president says 31,000 soldiers have been killed since Russia's full-scale invasion began.
Volodymyr Zelensky said he would not give the number of wounded as that would help Russian military planning.
Typically, Ukrainian officials do not make public the numbers of servicepeople killed in the war.
It comes after the defence minister said half of all Western aid for Ukraine has been delayed, costing lives and territory.
"At the moment, commitment does not constitute delivery," Rustam Umerov said in a televised address on Sunday.
Ukraine is currently experiencing a variety of setbacks in its mission to drive Russia from its territory.
Umerov said that the lack of supplies put Ukraine at a further disadvantage "in the mathematics of war".
"We do everything possible and impossible but without timely supply it harms us," he said.
German Defence Minister Boris Pistorius warned in November that plans to deliver a million artillery shells by March would not be met.
In January, the European Union (EU) said just over half of these would reach Ukraine by the deadline and that the full promised amount would not be there until the end of 2024.
The EU's foreign policy chief, Josep Borrell, blamed a lack of production capacity but Nato Secretary General Jens Stoltenberg said allies had been stepping this up.
Ukrainian forces have often complained of shortages in their war with Russia.
President Volodymyr Zelensky said one of the reasons Ukraine's highly anticipated counter-offensive did not start earlier last year was the lack of weapons.
That counter-offensive largely failed - one of a number of setbacks Kyiv has faced after some early successes in repelling Russia after it invaded in February 2022.
Last week, it was announced that troops had withdrawn from the key eastern town of Avdiivka - Moscow's biggest win in months.
Zelensky also blamed this partly on faltering Western weapon supplies.
The Biden administration, meanwhile, has said the hold-up in Congress of a US$60bn (NZ$97bn) aid package for Ukraine led to the fall of the town.
Despite the delay, Ukraine's prime minister sounded an optimistic note.
"We are deeply convinced that the United States will not abandon Ukraine in terms of both financial support and military, armed support," Denys Shmyal said on Sunday.
His comments come after Zelensky pressed members of the G7 - the world's richest democracies - to increase their "vital support" in order for his country to win the war.
"You know perfectly well that we need all this in time, and we count on you," he said at a virtual meeting.
Western leaders travelled to Kyiv on Saturday in a show of solidarity with Ukraine as the country marked two years since Russia's full-scale invasion.
There, it was announced that Italy and Canada had signed security deals with Ukraine - bolstering support until the country could join Nato.
Canada's deal included more than C$3bn (NZ$3.6bn) in financial and defence aid.
It is not only Ukraine that is having trouble resourcing its military activities. Russia is also struggling to provide ammunition and weapons, according to Western officials.
"Russia's domestic ammunition production capabilities are currently insufficient for meeting the needs of the Ukraine conflict," a Western official claimed.
They added that Moscow has been able to increase its supply only by seeking out alternative sources of ammunition and weapons, which do not offer a long-term solution.
Meanwhile, the head of Ukraine's security service said on Sunday that 47 Russian spy networks operating within Ukraine were uncovered last year.
Vasyl Maliuk added that more than 2000 suspected "traitors" have been arrested since Russia's full-scale invasion.
- This story was first published by the BBC.