Boris Johnson has launched a scathing attack on Russian President Vladimir Putin as the conflict continues in Ukraine.
Speaking in Warsaw, the Prime Minister said Mr Putin was using "barbaric and indiscriminate tactics against innocent civilians".
He added that the Russian president has "fatally underestimated" the resistance of the Ukrainian people and the resolve of the West to act while paying tribute to the "leadership and courage" of Ukrainian president Volodymyr Zelensky.
"Vladimir Putin is prepared to use barbaric and indiscriminate tactics against innocent civilians, to bomb tower blocks, to send missiles into tower blocks to kill children," Mr Johnson said.
Some have referred to Mr Johnson's comments as his "strongest remarks yet" against Mr Putin.
Mr Johnson said in the “grim war” Mr Putin had “fatally underestimated” the resistance of the Ukrainians and the resolve of the West to act.
He said Mr Putin was “tearing up every principle of civilised behaviour between states”.
“He has hurled his war machine on the people of Ukraine, a fellow Slavic country, he has bombarded civilian targets, fired rockets at blocks of flats, he is responsible for hundreds of civilian casualties including growing numbers of children.
“And also, of course, for the deaths of many Russian and Ukrainian soldiers.
“We must accept the grim reality that Putin will continue to tighten the vice and, if you go by the size and firepower of Vladimir Putin’s war machine, the odds have always been heavily against Ukrainian armed forces.”
He said Mr Putin had made a “colossal mistake” by invading Ukraine.
“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 also paid tribute to the “leadership and courage” of Volodymyr Zelensky, the Ukrainian president.
“I think he has inspired and mobilised not only his own people, he is inspiring and mobilising the world in outrage at what is happening in Ukraine,” Mr Johnson added.
Meanwhile, the Prime Minister said the Polish government and people were doing an "amazing job, an inspirational job" in addressing the humanitarian crisis resulting from the conflict.
He added: "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."
It comes as the British government faces increasing pressure from Tory and opposition MPs to implement more measures in taking in Ukrainian refugees.
Mr Johnson said more would be done to allow Ukrainians to come to the UK, with around 200,000 eligible under an expanded route for people to bring family members in.
Speaking in Warsaw, he said: “What we are going to do is we are extending the family scheme so that actually very considerable numbers would be eligible … you could be talking about a couple of hundred thousand, maybe more.
“Additionally, we are going to have a humanitarian scheme and then a scheme by which UK companies and citizens can sponsor individual Ukrainians to come to the UK.”
The Prime Minister also hinted at a new resettling scheme by working with Poland to help refugees, instead of having them claim asylum in the UK.
Mr Johnson told his Polish counterpart Mateusz Morawiecki: “We stand ready, clearly, to take Ukrainian refugees in our own country, working with you, in considerable numbers, as we always have done and always will.”
