Fears are growing Russian President Vladimir Putin could declare an "all-out war" on Ukraine in the coming days as revenge for humiliating military losses.
Russia has banned its media from using the term "war" and has called the invasion a "special military operation" to demilitarise and "denazify" Ukraine.
The UN said on Friday it had confirmed 2899 civilian deaths and 3235 injuries in Ukraine since Russia invaded its neighbouring country on February 24.
Of those killed, the UN has identified at least 210 children.
As the invasion goes into its 66th day, Russian army chiefs have called on Putin to officially declare a war on Ukraine.
A Russian military source told the Telegraph top military officials were "outraged that the blitz on Kyiv has failed".
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"People in the army are seeking payback for failures of the past and they want to go further in Ukraine," the official added.
If Putin did officially declare war on Ukraine it would enable mass mobilisation of the population, meaning reservists would be called up and conscripts would be kept beyond their one year term.
Putin would also have the ability to declare martial law, which would allow the closing of Russia’s borders and nationalisation of large chunks of the economy.
Ex-Nato chief Richard Sherriff has warned the West must prepare themselves for the "worst-case scenario" of Russia declaring war on Ukraine.
"The worst case is war with Russia. By gearing itself up for the worst case, it is most likely to deter Putin because ultimately Putin respects strength," he told BBC Radio 4.
UK Defence Secretary Ben Wallace has warned Putin might use Russia's Victory Day Parade on May 9 to announce the mass mobilisation of troops to Ukraine.
