Boris Johnson has accused Vladimir Putin of using “barbaric and indiscriminate tactics against innocent civilians” in Ukraine.
The prime minister, speaking on a visit to Warsaw alongside his Polish counterpart Mateusz Morawiecki, said the Russian President was prepared to “bomb tower blocks” and “kill children” as his army continued to face a fierce Ukrainian resistance in major cities.
The progress of the Russian Army has stalled in recent days, stoking fears Mr Putin could resort to brutal tactics in order to achieve his military objectives.
Reports emerged on Monday that cluster bombs and thermobarbaric weapons had been used by the Russian military - though this has not yet been officially confirmed.
Ukraine’s Foreign Minister Dmytro Kuleba condemned the “barbaric” attack on the eastern city of Kharkiv, where the Russian army launched a rocket strike on Independence Square.
Ukrainian officials claimed that dozens of people had been killed and residential areas targeted.
Mr Johnson vowed that Mr Putin’s “savagery” would be met with “unrelenting economic pressure”.
“Putin has lied to his people and to his troops about how this conflict would go, and he has now been caught out in that lie,” he said.
“They have not been welcomed to Ukraine as he prophesised, their tanks have not been cheered in the streets or garlanded with flowers.
“Instead, Ukrainians have mounted an astonishing and tenacious resistance.”
He said the west was ready for a “prolonged crisis” and that countries in Europe acknowledged that imposing sanctions would cause economic harm domestically.
“Putin has stubbed his toe and tripped on a giant immovable fact: no matter how many troops he sends, the Ukrainians want to live in a free and independent country,” he added.
Elsewhere, the prime minister hailed Poland’s “incredible” support for Ukraine and pledged further humanitarian support for those fleeing the Russian invasion.
“We in the UK stand ready to help you, we have humanitarian supplies already coming in - I think two planes of medical supplies have already landed, there is more to come,” Mr Johnson said.
