Russia has been accused of kidnapping children under the pretence of offering them 'assistance' as Putin's forces continue to fire on cities across the country.
The US embassy said Russian forces have illegally removed 2,389 Ukrainian children from the Donetsk and Luhanks oblasts to Russia.
In a tweet the US Embassy said: "According to the Ukrainian Foreign Ministry, Russian forces have illegally removed 2,389 Ukrainian children from Donetsk and Luhanks oblasts to Russia.
"This is not assistance. It is kidnapping."
Ukraine's human-rights spokesperson, Lyudmyla Denisova,, also alleged that Ukrainians were being "sent by rail to various economically depressed cities in Russia."
Mariupol Mayor Vadym Boichenko compared the removals of displaced Ukrainians to the work of the Nazis during World War II.
He told CNN: "What the occupiers are doing today is familiar to the older generation, who saw the horrific events of World War II when the Nazis forcibly captured people."
It comes after predictions Russia's supplies could only last another three days as Ukrainian continue in their strong counter-attack.
Vladimir Putin 's troops could run out of ammunition, food and fuel in a matter of days because of an inability to form a fuel pipeline, claimed the General Staff of the Armed Forces of Ukraine.
British Intelligence has said Russian attempts to capture Mariupol, viewed as a key target by Putin, "continue to be repulsed" as heavy fighting goes on.
Forces have been "largely stalled" elsewhere in Ukraine, including Kyiv, Chernihiv, Sumy and Kharkiv.
The assessment is in line with other Western allies' opinion that Russian supplies will run out this week and they will be forced to go on the defensive as they wait for more to arrive.
This "operational pause" will give Ukraine forces a chance to counter-attack.
This is something Ukrainian forces have already achieved in Makariv on the outskirts of Kyiv, capturing a key highway and blocking Russian soldiers from surrounding it to the northwest.
