Ukraine's First Lady Olena Zelenska has pleaded for "justice" against Russian aggression and for the UK to be a leader in the fight.
In a special address to MPs and peers on Monday evening, Mrs Zelenska urged politicians to support a call for a special tribunal to punish Moscow.
She said Ukraine had documented "thousands of crimes" by Russian forces with "torture chambers" found in many towns and villages.
In a harrowing speech, the First Lady said: "The youngest girl who was raped by the Russian occupiers was four years old. The oldest survivor was 85."
Nine months into the brutal invasion, she invoked the Blitz of the Second World War, saying: "Ukrainians are going through the terror, which will resonate with you.
"Your islands survived the air raids, which were identical to those that Russia uses now to put us on our knees.
"We're hearing sirens every day identical to those which were heard by earlier British generations. You did not surrender and we will not surrender."
In her speech - attended by former Prime Minister Boris Johnson and Labour leader Keir Starmer - Mrs Zelenska said "victory is not the only thing we need".
"We need justice," she told MPs and peers.
"We need to start the special tribunal against the crime of aggression of Russia against Ukraine, which will enhance the work of the ICC and not weaken it.
She added: "We need to unite the world community just as it happened in January 1942 to support the special tribunal against the aggression of Russia against Ukraine.
"I'm asking you a small favour to become the world leader in the justice efforts.
"I believe that London can give this decisive impetus so that the world can become better, fairer, thanks to you."
Earlier, Mrs Zelenska urged people not to forget the war in Ukraine this Christmas and the "tragedy" of the Russian invasion.
She also praised the UK's vocal support for the Ukrainian resistance efforts against Vladimir Putin's forces, as the country braces for winter
In an interview on BBC Radio 4's Today programme Mrs Zelenska said: "Ukrainians are very tired of this war, but we have no choice in the matter.
We are fighting for our very lives. The British public do have a choice… We do hope that the approaching season of Christmas doesn't make you forget about our tragedy and get used to our suffering."
