A senior United States official told ABC News that Russian soldiers had been overheard complaining that Ukrainian resistance was much stiffer than they had anticipated.
On one radio call, the official said they heard a soldier saying: “We don’t know who to shoot – they all look like us.”
Constantine Yevtushenko told the news site soldiers were hungry, were running low on supplies, and were confused about the purpose of their mission.
“They are just following the orders that they have,” Mr Yevtushenko said. “They are kids.”
Russian efforts to take the capital city of Kyiv have successfully been repelled for the past two nights by Ukrainian armed forces, although there were reports of an offensive being planned for Saturday night.
Thousands of citizens have also taken up arms and been encouraged to make home-made molotov cocktails.
There have been reports of more than 1,000 Russian soldiers being killed, and several hundred more captured.
On Saturday Ukrainian officials said 198 citizens – including three children – had been killed since the invasion began.
Health minister Viktor Liashko said that 1,115 people were injured including 33 children.